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Question DetailsAsked on 11/28/2017

I have a natural gas wall heater the pilot light will stay on till you turn gas on to it then it will burn 2 minute

I have a natural gas wall heater brand new when you light the pilot it stays on but when you turn the thermostat up an gas comes on it'll stay on 2 minutes then it will shut off everything any ideas

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First, since you said it is brand new, so if you had this installed by someone, call them back to fix it under warranty as defective work product. Or if you installed it yourself (though harder to enforce manufacturer warranty in that case because many require porofessional installation) contact the manufacturer.

Also google to see if that brand and model has a recall pending or a lot of complaints like yours.

Below are links to a few similar questions with answers which might help too, FYI - the first two sound similar to your case, the other two maybe not so much:

Because it is apparently consistently firing for 2 minutes before shutting down, does not sound like a direct in-line safety sensor shutting it down (like a pressure sensor or damper/eductor fan operation sensor on a high-effiency direct-vent water heater) - sounds more like something that takes a couple of minutes of heating / main burner running to create the condition nexcessary to cause it to shut down, like an overtemp or low oxygen sensor.

Likely causes of that which I have encountered - in no particular order:

1) air vent screen on water heater or air intake filter (some are now on the bottom - STUPID design) did not have protective paper or plastic film removed in installation, so it is running out of air once it burns up the air in the firebox and the low oxygen sensor is shutting it down.

2) metal cover over access port is not fully on, so it is getting extra/stray air currents from there which is disrupting the burning, causing flame rollout (flames getting beyond where it is supposed to be) or firebox overtemp sensor to trip out

3) flame rollout or firebox overtemp sensor is improperly positioned or malfunctioning, cutting off the gas supply after 2 minutes of operation changes firebox conditions enough to trip it out

4) thermocouple (or thermopile, whichever you have) is not properly in the pilot flame or the draft guard (the "finger" behind the flame) is improperly positioned, so when the main burner first fires up the thermocouple tip is heated properly and allows the gas to flow, but after the burner fires for awhile the incoming combustion air pulls the pilot flame away from the thermocouple or allows it to cool too much, which shuts off the gas flow because the gas control valve (by no longer getting the voltage from the thermocouple or thermopile) thinks the pilot has gone out

5) if you have a high efficiency heater (direct wall vent, plastic vent pipe) one of the safety sensors on that (like eductor fan operation, duct flapper valve opening, pressure differential sensor) may be malfunctioning or is too sensitive (generally not adjustable - if too sensitive or operating at wrong setpoint would notmally be a factory defect sensor)

6) rare, but exhaust blockage can do this - building up backpressure which eventually snuffs the flame with the exhaust gases which are not escaping out the flue

7) rare, but does occur more often with cheap thermocouples on the market these days - thermocouple/thermopile has gone bad and is too sensitive, shutting off when it heats up additionally from the main burner heat

8) temperature setting is at lowest / Vacation setting - a few furnaces/boilers/high-end water heaters have a periodic condensate reduction cycle which runs the main burner for a couple of minutes periodically when at lowest setting (sometimes every so many hours since last run cycle regardless of setting as long as below thermostat temperature setting) to keep the condensation and cobwebs and such in control in the firebox area and to keep the water at least warm as protection against freezing in winter. Could be it is running that minimum cycle time and then shutting down because the thermostat is saying it does not need to heat the water any more. Turning thermostat down to minimum then back up to a higher setting than originally (so it detects that the water is cooler than thermostat is set for) might defeat this if it is stuck in that mode - could be restarting that minimum run time each time you start it back up just becuase the water is already up to temp, so it is not running longer.

9) check the gas supply shutoff valve (usually where metal or smooth plastic gas supply line connects to flex tubing to heater) got reopened all the way - if is was only cracked open a bit (commonly done to test connections during setup so you don't get a major gas flow if there is a leak) maybe the tech forgot to then turn it all the way on (aligned straight with the gas pipe it is on), so there might be enough gas pressure in the system and flex tubing to start the heater, but it then runs low on pressure after running a bit and the low-pressure shutoff in the gas control valve is shutting it down - that will usually (but not always) cut out the pilot as well as main burner gas flow.

10) rare, but does happen with some makes - thermocouple/thermopile uses a frame neutral and is either not securely mounted/screwed into the pilot housing/bracket so is not making good electrical contact, or is touching metal along the way back to the gas control valve so is losing some of its power. Ditto if thermocouple uses outer copper surface as neutral/return (common) and it is touching metal along the run, and interrupting the power for the gas control valve or picking up a neutralizing static charge - I have encountered this frame-contact problem enough times over the years to make it one of the first things I look for in the case of malfunctioning thermocouple/thermopiles.

11) rare, but also happens - thermocouple tubing is routed too close to main burner (much more common with tube burners on furnaces/boilers) so it is overheating and failing

12) happening more often with cheap Chinese valves, from building trades hearsay - my go-plumber says he is hitting this monthly or more often as opposed to maybe once every few years in the old days - faulty gas control valve on new water heater cutting out after a short period of use or even right at initial installation

13) sometimes, but I would not expect it to have a consistent run time before cutout each time, is if the thermocouple / thermopile is not making good contact inside the gas control valve. Sometimes if the threaded collar which holds it in is kept tight up against the valve as the thermocouple/thermopile tip is inserted, the tip gets jammed in the threads - the right way is to straigten the tubing at that end, slide the threaded collar or bushing back a few inches, insert the straight tubing/tip all the way up into the "well" to make good tip contat, then holding that screw the threaded bushing into the well and lightly snug it in. Over tightening (more than just firmly had snug or VERY light wrench tightening) can also sometimes smush (good technical term there) the solder tip out enough to ground it out to the housing, causing intermittent or complete pilot gas failure.

Debugging would take several steps -

- I would first ask if the pilot is going out or not - if so, generally (not universally) the safety cutouts only stop the main burner gas flow, not the pilot - so if pilot is going out too I would suspect the thermocouple or how far it is into the pilot flame or if pilot flame is being diverted from it when the main burner is on. Owners Manual may say if safety devices cut off pilot too or only main burner - might give a clue as to the source of the shutdown. Manuals also usually have at least a simple owners troubleshooting guide in them.

- Second, I would next be taking a volt-ohm meter and, immediately after it cuts out, check for power continuity across the various safety sensors (should be listed on parts list) to see if one of them is cutting out. (Since it is restarting each time, I would be looking for self-resetting safety cutout sensors, not any which are once-fail type which have to be replaced after cutting out (like some flame rollout and firebox overtemp sensors with some brands), because obviously it is not caused by a once-fail cutout. If your water heater has LED indicator lights on it check manual for what the light color or blinking pattern means (some have multiple lights which illuminate in different combinations to show a "code", others have different "blink" patterns.)

If it runs pretty consistent amount of time before shutting down on multiple attempts, I would VERY strongly suspect a safety sensor is causing it to shut down or gas valve not fully open - since it is apparently running a fixed amount of time each time.

Answered 2 years ago by LCD

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