EP3327351B1

EP3327351B1 - Method for operating a fan assisted, atmospheric gas burner appliance

Info

Publication number: EP3327351B1
Application number: EP16200264.6A
Authority: EP
Inventors: Umberto Corti; Massimo CONTI; Marco Spelzini
Original assignee: Honeywell Technologies SARL
Current assignee: Garrett Motion SARL
Priority date: 2016-11-23
Filing date: 2016-11-23
Publication date: 2019-10-09
Anticipated expiration: 2036-11-23
Also published as: EP3327351A1

Description

The present patent application relates to methods for operating a fan assisted, atmospheric gas burner appliance.
Gas burner appliances are differentiated between standard efficiency gas burner appliances and high efficiency gas burner appliances. Standard efficiency (SE) gas burner appliances are also called fan assisted, atmospheric gas burner appliances. High efficiency (HE) gas burner appliances are also called premix gas burner appliances. The invention is related to fan assisted, atmospheric gas burner appliances only.
Fan assisted, atmospheric gas burner appliances comprise a burner chamber. A gas/air mixture can be combusted or burned within said burner chamber when the gas burner and thereby the gas/air mixture is ignited. Fan assisted, atmospheric gas burner appliances further comprise a heat exchanger for heating water by combusting or burning said gas/air mixture within said burner chamber. The water entering into the heat exchanger is often called return-flow water and the water exiting the heat exchanger is often called forward-flow water. Fan assisted, atmospheric gas burner appliances further comprise an air pipe or air duct for providing the air of the gas/air mixture, a gas pipe or gas duct for providing the gas of the gas/air mixture and an exhaust pipe or exhaust duct through which exhaust flowing out of the burner chamber can emerge into the ambient of the gas burner. Fan assisted, atmospheric gas burner appliances also comprise a fan being assigned to the exhaust pipe or the air pipe and a gas valve being assigned to the gas pipe. For modulation of the burner load of a fan assisted, atmospheric gas burner appliance the valve position of the gas valve is changed while the speed of the fan is kept constant or almost constant.
The gas supply pressure for a fan assisted, atmospheric gas burner appliance may be subject of disturbances. Specifically, the actual gas supply pressure may drop below a nominal gas supply pressure being necessary to ensure a stable operation of the fan assisted, atmospheric gas burner appliance. Further on, the operation of a fan assisted, atmospheric gas burner appliance may be disturbed by an obstructed exhaust pipe and/or an obstructed air pipe.
According to the prior art, individual sensors are required to detect if the actual gas supply pressure corresponds to the nominal gas supply pressure and to detect if the exhaust pipe and/or the air pipe is obstructed. According to the prior art, gas pressure sensors assigned to the gas pipe are used to measure the actual gas supply pressure. Air pressure switches are used to detect the flow through the exhaust pipe and thereby to determine if the exhaust pipe and/or air pipe is obstructed. The use of such sensors is adding costs to the appliance.
EP 2 447 609 B1 discloses a method for operating a fan assisted, atmospheric gas burner appliance. According to EP 2 447 609 B1 a measurement signal of a temperature sensor measuring the exhaust temperature in combination with a measurement signal of an flame ionization sensor is used to determine the opening and/or closing status of the exhaust pipe and/or air pipe, whereby at a burner start up when the gas burner becomes ignited the fan is operated at maximum fan speed and a first exhaust temperature value is measured by said exhaust temperature sensor and a first ionization current value is measured by said flame ionization sensor, whereby after a defined time period the fan is operated at a lower fan speed and a second exhaust temperature value is measured by said exhaust temperature sensor and a second ionization current value is measured by said flame ionization sensor, and whereby when a difference between said first exhaust temperature value and said second exhaust temperature value and a difference between said first ionization current value and said second ionization current value are both relatively big or high, the exhaust pipe and/or air pipe is in a opened status, preferably in a fully opened status.
Against this background, novel methods for operating a fan assisted, atmospheric gas burner are provided, namely methods for checking the gas supply pressure and the status of the exhaust pipe on basis of one sensor signal only, namely on basis of the measurement signal of the flame ionization sensor.
A first method according to the present application is defined in the claim 1.
During active combustion of the gas/air mixture while the fan is running at a first fan speed and while the valve position of the gas valve is a at first valve position, the fan speed of the fan will be decreased to a second fan speed, the valve position of the gas valve will be kept constant or almost constant and the change of the measurement signal of the flame ionization sensor will be monitored over a defined time period after the decrease of the fan speed. After said defined time period, the fan speed of the fan will be increased, the valve position of the gas valve will be decreased and the subsequent change measurement signal of the flame ionization sensor will be monitored. If the change of the measurement signal of the flame ionization sensor is smaller than a threshold after the decrease of the fan speed of the fan to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor is smaller than a threshold after the increase of the fan speed of the fan and the decrease of the valve position of the gas valve, an actual gas supply pressure in the gas pipe being smaller than a nominal gas supply pressure. However, if the change of the measurement signal of the flame ionization sensor is greater than the threshold after the decrease of the fan speed of the fan to the second fan speed, an actual gas supply pressure in the gas pipe corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe and an unobstructed air pipe is detected.
A second method according to the present application is defined in the claim 2.
During active combustion of the gas/air mixture while the fan is running at a first fan speed and while the valve position of the gas valve is a at first valve position, the fan speed of the fan will be decreased to a second fan speed, the valve position of the gas valve will be kept constant or almost constant and the change of the measurement signal of the flame ionization sensor will be monitored over a defined time period after the decrease of the fan speed. After said defined time period, the fan speed of the fan will be increased, the valve position of the gas valve will be decreased and the subsequent change measurement signal of the flame ionization sensor will be monitored. If the change of the measurement signal of the flame ionization sensor is smaller than a threshold after the decrease of the fan speed of the fan to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor is greater than a threshold after the increase of the fan speed of the fan and the decrease of the valve position of the gas valve, an obstructed exhaust pipe and/or obstructed air pipe is detected. If the change of the measurement signal of the flame ionization sensor is greater than the threshold after the decrease of the fan speed to the second fan speed, an actual gas supply pressure in the gas pipe corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe and unobstructed air pipe is detected.
The methods provide a reliable way to determine the gas supply pressure and the status of the exhaust pipe using one sensor signal only, namely the measurement signal of the flame ionization sensor.
If the change of the measurement signal of the flame ionization sensor is greater than the threshold after the decrease of the fan speed of the fan to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor is greater than a threshold after the increase of the fan speed of the fan and the decrease of the valve position of the gas valve, an actual gas supply pressure corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe and an unobstructed air pipe is detected. The methods according to the present invention provide a reliable way to determine the gas supply pressure and the status of the exhaust pipe on basis of one sensor signal only, namely on basis of the measurement signal of the flame ionization sensor.
Preferred developments of the invention are provided by the dependent claims and the description which follows. Exemplary embodiments are explained in more detail on the basis of the drawing, in which:

Figure 1: shows a schematic view of a fan assisted, atmospheric gas burner appliance;
Figure 2: shows a schematic view of another fan assisted, atmospheric gas burner appliance;
Figure 3: shows signals illustrating the present invention;
Figure 4: shows further signals further illustrating the present invention; and
Figure 5: shows further signals further illustrating the present invention.

The present invention relates to methods for operating a fan assisted, atmospheric gas burner appliance.
Figures 1 and 2 show both a schematic drawing of a fan assisted, atmospheric gas burner appliance 10. A fan assisted, atmospheric gas burner appliance is also called standard efficiency (SE) gas burner appliance.
Such a fan assisted, atmospheric gas burner appliance 10 comprises a burner chamber 11 in which a gas/air mixture can be combusted or burned. Such a fan assisted, atmospheric gas burner appliance 10 further comprises a heat exchanger 12 for heating water by combusting or burning said gas/air mixture. Water 13 entering into the heat exchanger 12 is often called return-flow water 13 and water 14 exiting the heat exchanger 12 is often called forward-flow water 14.
Such a fan assisted, atmospheric gas burner appliance 10 further comprises an air pipe 15 or air duct for providing the air of the gas/air mixture, a gas pipe 16 or gas duct for providing the gas of the gas/air mixture and an exhaust pipe 17 or exhaust duct through which exhaust flowing out of said burner chamber 11 can emerge into the ambient of the gas burner 10 appliance.
A gas valve 18 is assigned the gas pipe 16 for adjusting the gas flow through the gas pipe 16. The fan assisted, atmospheric gas burner appliance 10 further comprises a fan 19. In Figure 1 said fan 19 is assigned to the exhaust pipe 17. In Figure 2 said fan 19 is assigned to the air pipe 15. The combustion of the gas/air mixture within the burner chamber 11 results into flames 20.
The exhaust pipe 17 emerges preferably at a roof wall 22 of the burner chamber 11 from the same. The exhaust pipe 17 is mounted to the burner chamber 11 at a flange or hock 23 of the roof wall 22.
A flame ionization sensor 24 of the fan assisted, atmospheric gas burner appliance 10 is positioned preferably within the burner chamber 11 in the region of the flames 20 originating when combusting the gas/air mixture. The flame ionization sensor 24 provides as measurement signal an electrical current or electrical voltage which depends on the burner load.
During operation of the fan assisted, atmospheric gas burner appliance 10 the modulation of the burner load is effected by adjusting the valve position of the gas valve 19 while the fan speed of the fan 19 is kept constant or almost constant. An almost constant fan speed means that the variation of the fan speed of the fan 19 is smaller than a defined threshold.
To ensure a stable operation of the fan assisted, atmospheric gas burner appliance 10 the actual gas supply pressure within the gas pipe 16 upstream of the gas valve 18 shall correspond to a nominal gas supply pressure. Further on, to ensure a stable operation of the fan assisted atmospheric gas burner appliance 10 the exhaust pipe 17 and the air pipe 15 shall both not be obstructed.
The methods according to the present invention provide a reliable way to determine the gas supply pressure and the status of the exhaust pipe on basis of one sensor signal only, namely on basis of the measurement signal of the flame ionization sensor 24.
During active combustion of the gas/air mixture within the burner chamber 11 of the fan assisted, atmospheric gas burner appliance 10 while the fan 19 is running at a first fan speed and while the valve position of the gas valve 16 is a at first valve position of the gas valve 18, the fan speed of the fan 19 will be decreased to a second fan speed and the change of the measurement signal of the flame ionization sensor 24 will be monitored.
If the caused change of the measurement signal of the flame ionization sensor 24 is smaller than a threshold after the decrease of the fan speed of the fan 19 to the second fan speed, the method detects an actual gas supply pressure in the gas pipe 16 being smaller than a nominal gas supply pressure or an obstructed exhaust pipe 17 and/or obstructed air pipe 15. However, if the change of the measurement signal of the flame ionization sensor 24 is greater than the threshold after the decrease of the fan speed of the fan 19 to the second fan speed, the method detects an actual gas supply pressure in the gas pipe 16 corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe 17 and an unobstructed air pipe 15.
Further details of the methods according to the present invention are discussed below with reference to Figures 3 to 5. Figures 3 to 5 all show time curves of the signals 25, 26 and 27.
The signal 25 (dashed curve) is a fan speed signal illustrating over the time t the fan speed at which the fan 19 is running.
The signal 26 (dotted curve) is a valve position signal illustrating over the time t the valve position of the gas valve 18 and thereby the modulation of the burner load.
The signal 27 (dot-dashed curve) is the measurement signal provided by the flame ionization sensor 24 over the time t.
Figure 3 illustrates an exemplary operation status of the a fan assisted, atmospheric gas burner appliance 10 in which an actual gas supply pressure in the gas pipe 16 being smaller than a nominal gas supply pressure becomes detected.
In Figure 3 a heat demand occurs at point of time t0 and the atmospheric gas burner appliance 10 becomes started up. First, at point of time t0 the fan 19 will be started so that the fan 19 runs with a first fan speed n1, preferably with maximum fan speed. Then, at point of time t1 the gas valve 18 will be opened to a valve position x1 corresponding to a modulation of the burner loads required to fulfill the heat demand. Further on, at point of time t1 the gas burner and thereby the gas/air mixture becomes ignited so that the gas/air mixture will be combusted within the burner chamber 11.
The flames 20 resulting from that combustion cause that the flame ionization sensor 24 provides the measurement signal 27.
If during active combustion of the gas/air mixture the fan 19 is running at the first fan speed n1 and the valve position of the gas valve 16 is at the first valve position x1 corresponding to the modulation of the burner loads required to fulfill the heat demand, but the gas burner appliance 10 does not provide the required heat demand, e.g. by not providing the required forward-flow water temperature, the fan speed 25 of the fan 19 will be decreased at point of time t2 to a second fan speed n2 while the valve position of the gas valve 18 is kept constant or almost constant and the change of the measurement signal of the flame ionization sensor 24 will be monitored, preferably the change of the measurement signal compared with the value of the measurement signal at point of time t2 at which the fan speed becomes decreased.
An almost constant valve position of the gas valve 18 means that the variation of the valve position is smaller than a defined threshold.
So, when the fan speed of the fan 19 becomes decreased at point of time t2 from the first fan speed n1 to second fan speed n2, the valve position of the gas valve 18 is kept constant and the change of the measurement signal 27 of the flame ionization sensor 24 will be monitored over a defined period of time Δt.
The first fan speed n1 of the fan 19 is preferably the maximum fan speed. The second fan speed n2 of the fan 19 is smaller than the first fan speed n1 but preferably larger than zero. However, depending from the gas burner appliance the second fan speed n2 can also be equal zero.
The second fan speed n2 of the fan 19 is in the range between 50% and 90%, preferably in the range between 60% and 80%, most preferably in the range between 65% and 75%, of the first fan speed n1.
In Figure 3 the change of the measurement signal 27 of the flame ionization sensor 24 after the decrease of the fan speed of the fan 19 to the second fan speed at point of time t2 is smaller than a first threshold. So, either an actual gas supply pressure in the gas pipe 16 being smaller than a nominal gas supply pressure or an obstructed exhaust pipe 17 and/or an obstructed air pipe 15 becomes detected.
After the defined period of time Δt, the fan speed of the fan 19 will be increased at point of time t3 and at the same point of time t3 or immediately after the point of time t3 the valve position of the gas valve 18 will be decreased. Further on, the subsequent change measurement signal 27 of the flame ionization sensor 24 will be monitored, preferably the subsequent change of the measurement signal compared with the value of the measurement signal at point of time t3 at which the fan speed becomes increased and the valve position of the gas valve 18 becomes decreased.
As shown in Figure 3, at point of time t3 the fan speed 25 of the fan 19 will preferably be increased back to the first fan speed n1 and the gas valve 18 will preferably be completely closed by changing the first valve position x1 to the second valve position x2. The resulting subsequent change of measurement signal 27 from of the flame ionization sensor 24 will be monitored.
If the change of the measurement signal of the flame ionization sensor 24 is smaller than the first threshold after the decrease of the fan speed of the fan 19 to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor 24 is smaller than a second threshold after the increase of the fan speed of the fan 19 and the decrease of the valve position of the gas valve 18 (see Figure 3), an actual gas supply pressure being smaller than a nominal gas supply pressure is detected.
With this detection result, namely with the detection of a gas supply pressure being smaller than a nominal gas supply pressure, the valve position 26 of the gas valve 18 is changed back at point of time t4 to the first valve position x1. The gas burner appliance is allowed for continued combustion because the combustion is not toxic with a CO content (e.g. 2000 ppm) within the exhaust gas smaller than a defined threshold.
However if the change of the measurement signal of the flame ionization sensor 24, preferably the change of the measurement signal compared with the value of the measurement signal at point of time t2, is smaller than the first threshold after the decrease of the fan speed of the fan 19 to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor 24, preferably the subsequent change of the measurement signal compared with the value of the measurement signal at point of time t3, is greater than the second threshold after the increase of the fan speed of the fan 19 and the decrease of the valve position of the gas valve 18 (see Figure 4), an obstructed exhaust pipe 19 and/or obstructed air pipe 15 is detected.
With this detection result, namely with the detection of an obstructed exhaust pipe 27 and/or an obstructed air pipe 15, the valve position 26 of the gas valve 18 is kept at the completely closed position x2 and the fan speed 25 of the fan 19 is reduced to zero so that at point of time t4 to gas burner appliance 10 is shut down. The gas burner appliance is not allowed for continued combustion because the combustion is toxic with a CO content within the exhaust gas greater than the defined threshold. The second threshold corresponds preferably to the first threshold.
Up to point of time t3 the curves 25, 26 and 27 of Figure 3 and the curves 25, 26 and 27 of Figure 4 are almost identical. Only the absolute magnitude of the measurement signal 27 of the flame ionization sensor 24 is different.
However, the methods according to the present invention are not based on the absolute magnitude of the measurement signal 27 of the flame ionization sensor 24 but on the change on the measurement signal 27 and thereby on the relative magnitude of the same.
In the operation status of Figure 3 and in the operation status of Figure 4 the change of the measurement signal 27 of the flame ionization sensor 24 is smaller than the first threshold after the decrease of the fan speed 25 of the fan 19 at point of time t2 from the first fan speed n1 to the second fan speed n2 while the valve position 26 of the gas valve 18 and thereby the modulation has been kept constant at point of time t2. So after point of time t2 and before point of time t3 either an actual gas supply pressure being smaller than a nominal gas supply pressure or an obstructed exhaust pipe 17 and/or obstructed air pipe 15 will be detected. In order to differentiate between i) an actual gas supply pressure being smaller than a nominal gas supply pressure and ii) an obstructed exhaust pipe 17 and/or obstructed air pipe 15, after the time period Δt at point of time t3 the fan speed 25 will be increased and the valve position of the gas valve 18 will be decreased.
The fan speed 25 of the fan 19 becomes preferably increased back to the first fan speed n1 and the gas valve becomes preferably completely closed at point of time t3.
If then the subsequent change of the measurement signal 27 of the flame ionization sensor 24 is smaller than a second threshold, an actual gas supply pressure being smaller than a nominal gas supply pressure is detected.
However, if then the subsequent change of the measurement signal 27 of the flame ionization sensor 24 is greater than the second threshold, an obstructed exhaust pipe 17 and/or obstructed air pipe 15 will be detected. The second threshold corresponds preferably to the first threshold.
Figure 5 illustrates an exemplary operation status of the fan assisted, atmospheric gas burner appliance 10 in which the actual gas supply pressure in the gas pipe 16 corresponds to the nominal gas supply pressure and in which further the exhaust pipe 17 and the air pipe 15 are both unobstructed.
In Figure 5 a heat demand occurs at point of time t0 and the atmospheric gas burner appliance 10 becomes started up.
First, at point of time t0 the fan 19 will be started so that the fan 19 runs with a first fan speed n1, preferably with maximum fan speed. Then, at point of time t1 the gas valve 18 will be opened to a valve position x1 corresponding to the modulation of the gas burner required to fulfill the required heat demand.
Further on, at point of time t1 the gas burner or gas/air mixture becomes ignited so that the gas/air mixture will be combusted within the burner chamber 11. The flames 20 resulting from that combustion cause that the flame ionization sensor 24 provides the measurement signal 27.
If during active combustion of the gas/air mixture the fan 19 is running at the first fan speed n1 and the valve position of the gas valve 16 is at the first valve position x1 but the gas burner appliance 10 does not provide the required heat demand, e.g. by not providing the required forward-flow water temperature, the fan speed 25 of the fan 19 will be decreased at point of time t2 to a second fan speed n2 while the valve position of the gas valve 18 is kept constant or almost constant.
The change of the measurement signal of the flame ionization sensor 24 will be monitored, preferably the change of the measurement signal compared with the value of the measurement signal at point of time t2.
So, when the fan speed of the fan 19 becomes decreased at point of time t2 from the first fan speed n1 to the second fan speed n2, the valve position of the gas valve 18 is kept constant and the change measurement signal 27 provided by the flame ionization sensor 24 will be monitored.
In Figure 5 the change of the measurement signal 27 of the flame ionization sensor 24 after the decrease of the fan speed of the fan 19 to the second fan speed at point of time t2, preferably the change of the measurement signal compared with the value of the measurement signal at point of time t2, is greater than the first threshold. So, neither an actual gas supply pressure in the gas pipe 16 being smaller than a nominal gas supply pressure nor an obstructed exhaust pipe 17 nor an obstructed air pipe 15 becomes detected.
After the defined time period Δt, the fan speed of the fan 19 will be increased at point of time t3 and at the same point of time t3 or immediately after the point of time t3 the valve position of the gas valve 18 will be decreased. Further on, the subsequent change of the measurement signal 27 of the flame ionization sensor 24 will be monitored, preferably the subsequent change of the measurement signal compared with the value of the measurement signal at point of time t3.
As shown in Figure 5, at point of time t3 the fan speed 25 of the fan 19 is increased back to the first fan speed n1 and the gas valve 18 will be completely closed by changing the first valve position x1 to the second valve position x2. The resulting change of measurement signal 27 from of the flame ionization sensor 24 will be monitored.
If the subsequent change of the measurement signal 27 of the flame ionization sensor 24 is greater than the second threshold after the increase of the fan speed of the fan 19 and after the decrease of the valve position of the gas valve 18, an actual gas supply pressure corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe and an unobstructed air pipe is detected. With this detection result the valve position 26 of the gas valve 18 is changed back at point of time t4 to the first valve position x2. At point of time t5 the heat demand and modulation changes. The gas burner appliance is allowed for continued combustion because the combustion is not toxic with a CO within the exhaust gas content smaller than the defined threshold.
If the change of the measurement signal 27 of the flame ionization sensor 24 after the decrease of the fan speed of the fan 19 to the second fan speed at point of time t2 is greater than the first threshold and if further the subsequent change of the measurement signal 27 of the flame ionization sensor 24 is smaller than the second threshold after the increase of the fan speed of the fan 19 and after the decrease of the valve position of the gas valve 18, the burner will be restarted or shut-down after a defined number of restarts.
As A-mentioned above, the methods according to the present invention are performed during active combustion of the gas/air mixture serving a required heat demand if the fan 19 is running at a first fan speed, if the valve position of the gas valve 16 is a at first valve position depending from the required heat demand and if the gas burner appliance 10 does not provide the required heat demand by not providing a required nominal forward-flow water temperature of the heat exchanger 12.

List of reference signs

10: gas burner appliance
11: burner chamber
12: heat exchanger
13: return-flow water
14: forward flow water
15: air pipe / air duct
16: gas pipe / gas duct
17: gas valve
19: fan
20: flame
21: exhaust outlet
22: roof wall
23: flange / hook
24: flame ionization sensor
25: fan speed signal
26: valve position signal
27: measurement signal of the flame ionization sensor

Claims

Method for operating a fan assisted, atmospheric gas burner appliance (10),
said gas burner appliance (10) comprising a burner chamber (11) in which a gas/air mixture can be combusted,

said gas burner appliance (10) further comprising a heat exchanger (12) for heating water by combusting said gas/air mixture,

said gas burner appliance (10) further comprising an air pipe (15) or air duct for providing the air of the gas/air mixture, a gas pipe (16) or gas duct for providing the gas of the gas/air mixture and an exhaust pipe (17) or exhaust duct through which exhaust flowing out of said burner chamber (11) can emerge into the ambient of the gas burner appliance,

said gas burner appliance (10) further comprising a fan (19) being assigned to the exhaust pipe (17) or to the air pipe (15) and a gas valve (18) being assigned to the gas pipe (16), wherein for modulation of the burner load the valve position of the gas valve (18) is changed,

said gas burner appliance (10) further comprising a flame ionization sensor (24) providing a measurement signal,

wherein

during active combustion of the gas/air mixture while the fan (19) is running at a first fan speed and while the valve position of the gas valve (18) is a at first valve position, the fan speed of the fan (19) will be decreased to a second fan speed, the valve position of the gas valve (18) will be kept constant or almost constant and the change of the measurement signal of the flame ionization sensor (24) will be monitored over a defined time period after the decrease of the fan speed,

after said defined time period, the fan speed of the fan (19) will be increased, the valve position of the gas valve (18) will be decreased and the subsequent change measurement signal of the flame ionization sensor (24) will be monitored,

if the change of the measurement signal of the flame ionization sensor (24) is smaller than a threshold after the decrease of the fan speed of the fan (19) to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor (24) is smaller than a second threshold after the increase of the fan speed of the fan (19) and the decrease of the valve position of the gas valve (18), an actual gas supply pressure in the gas pipe (16) being smaller than a nominal gas supply pressure is detected,

if the change of the measurement signal of the flame ionization sensor (24) is greater than the threshold after the decrease of the fan speed to the second fan speed, an actual gas supply pressure in the gas pipe (16) corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe (17) and unobstructed air pipe (15) is detected.
Method for operating a fan assisted, atmospheric gas burner appliance (10),
said gas burner appliance (10) comprising a burner chamber (11) in which a gas/air mixture can be combusted,

said gas burner appliance (10) further comprising a heat exchanger (12) for heating water by combusting said gas/air mixture,

said gas burner appliance (10) further comprising an air pipe (15) or air duct for providing the air of the gas/air mixture, a gas pipe (16) or gas duct for providing the gas of the gas/air mixture and an exhaust pipe (17) or exhaust duct through which exhaust flowing out of said burner chamber (11) can emerge into the ambient of the gas burner appliance,

said gas burner appliance (10) further comprising a fan (19) being assigned to the exhaust pipe (17) or to the air pipe (15) and a gas valve (18) being assigned to the gas pipe (16), wherein for modulation of the burner load the valve position of the gas valve (18) is changed,

said gas burner appliance (10) further comprising a flame ionization sensor (24) providing a measurement signal,

wherein

during active combustion of the gas/air mixture while the fan (19) is running at a first fan speed and while the valve position of the gas valve (18) is a at first valve position, the fan speed of the fan (19) will be decreased to a second fan speed, the valve position of the gas valve (18) will be kept constant or almost constant and the change of the measurement signal of the flame ionization sensor (24) will be monitored over a defined time period after the decrease of the fan speed,

after said defined time period, the fan speed of the fan (19) will be increased, the valve position of the gas valve (18) will be decreased and the subsequent change measurement signal of the flame ionization sensor (24) will be monitored,

if the change of the measurement signal of the flame ionization sensor (24) is smaller than a threshold after the decrease of the fan speed of the fan (19) to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor (24) is greater than a second threshold after the increase of the fan speed of the fan (19) and the decrease of the valve position of the gas valve (18), an obstructed exhaust pipe (17) and/or obstructed air pipe (15) is detected,

if the change of the measurement signal of the flame ionization sensor (24) is greater than the threshold after the decrease of the fan speed to the second fan speed, an actual gas supply pressure in the gas pipe (16) corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe (17) and unobstructed air pipe (15) is detected.
Method as claimed claim 1 or 2, characterized in that if the change of the measurement signal of the flame ionization sensor (24) is greater than the threshold after the decrease of the fan speed of the fan (19) to the second fan speed, and if the subsequent change of the measurement signal of the flame ionization sensor (24) is greater than the second threshold after the increase of the fan speed of the fan (19) and the decrease of the valve position of the gas valve (18), an actual gas supply pressure corresponding to the nominal gas supply pressure and an unobstructed exhaust pipe and an unobstructed air pipe (15) is detected.
Method as claimed in one of claims 1 to 3, characterized in that after said defined time period the valve position of the gas valve (18) will be decreased is such a way that the gas valve (18) will be completely closed.
Method as claimed in one of claims 1 to 4, characterized in that after said defined time period the fan speed of the fan (19) will be increased to the first fan speed.
Method as claimed in one of claims 1 to 5, characterized in that the first fan speed of the fan (19) is the maximum fan speed and the second fan speed of the fan (19) is preferably larger than zero.
Method as claimed in one of claims 1 to 6, characterized in that the second fan speed of the fan (19) is in the range between 50% and 90%, preferably in the range between 60% and 80%, most preferably in the range between 65% and 75%, of the first fan speed of the fan (19).
Method as claimed in one of claims 1 to 7, characterized in that the same will be performed after each burner start up.
Method as claimed in one of claims 1 to 7, characterized in that the same will be performed during active combustion of the gas/air mixture serving a required heat demand if the gas burner appliance (10) does not provide the required heat demand by not providing a nominal forward-flow water temperature of the heat exchanger (12).