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Question DetailsAsked on 11/9/2014

I had turned on thermostat & the gas burner won't kick on.

Lit pilot light on gas burner, turned thermostat on & burner does nothing.

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3 Answers


After lighting pilot, you need to turn the valve to on for the burner to light. You likely know this, but just in case.

If you did that, thenyou'll need a service tech, find the best of the best on Angie's List!


Answered 5 years ago by BayAreaAC


Here are a couple of previous responses to that question - more can be found in the Home > HVAC link in Browse Projects, at lower left.

Not knowing how ancient or modern your furnace is, there are several likely causes - some covered in the referenced response above, some not. I am going to assume here the pilot light stayed lit OK, which probably means the thermocouple is OK too - but not always. If pilot will not stay lit (after holding PILOT or LIGHT button down for 30-60 seconds before releasing to give thermocouple chance to heat up in the pilot flame, because till it is hot the pilot light will not stay lit when button is released except on ancient furnaces), then the problem is almost always the thermocouple needs changing. Commonly recommended to be changed yearly, even though they can last 3-10+ years at times and you might tolerate unplannedfailure with a water heater, but annual furnace thermocouple changout is the easiest way (for about $10-15 part cost typically) to avoid mid-winter breakdowns, and changing it out is commonly a standard part of the flat seasonal cleaning/servicing fee of about $75-150.

Common causes of your issue:

1) power switch or breaker to furnace is off, or low voltage wire from transformer to control box is broken or disconnected

2) thermostat set below current room temp or thinks it is a set-back time when room temp is supposed to be lower than current room temp is, so it thinks it is not supposed to turn on - try temporarily setting significantly higher than current room temp. Other possibility - batteries died or were changed out and thermostat rebooted to factory default settings (if electronic) which say current room temp is high enough - typically 68 degrees F but sometimes lower. In that case, thermostat needs to be "re-taught" the desired cycles throughout the week.

3) thermostat function switch still set to OFF or AC (air conditioner) - need to be set to HEAT or similar phrased setting

4) thermostat batteries dead or nearly so

5) thermostat wire to furnace got damaged or broken - usually right at connection point to controller, or to zone valve if hydronic (hot water) or steam system, or cut or shorted buy being pinched by furnace metal casing where it passes through it, or by insulation melting due to contact with hot ducting or hydronic system piping.

6) gas control knob on controller not fully set to on - many have a safety detent that will not let it be turned to on from the PILOT position unless it is pushed in while turning so it may turn a ways but not far enough to turn on - try turning back to PILOT, then after checking if it will push in (about 1/4-1/2 inch) turn to ON. Others CANNOT be pushed in while turning (as opposed to pilot setting wehich is pushed in) so if pushing down while turning will not turn to ON position even if it does turn a bit.

7) some safety interlock or sensor is not working right or is corroded up, electric controlled damper not opening, or fan failed to kick on so burner will not fire due to safety interlocks

8) gas not getting to appliance in full pressure - low gas pressure (if on tanked gas) or mostly closed gas shutoff valve or meter that was not fully reopened after a service action. This is rare - if gas dryer or stove or water heater works fine and shutoff valve leading to furnace is open (handle or tab aligned with the pipe), then not the problem.

9) very rarely, but a real pain to figure out when it happens - water in the gas piping exceeded capacity of drip leg and is blocking gas flow, which is VERY low pressure so can overcome only about 7 inches of water standing in the pipe - not enough to get to the furnace in almost all piping configurations. Plus if there is water in the piping the filter in the gas controller should block the flow into the controller - hence no gas to the burners.

10) &(*&%##^ electronic furnace controller or sensor failed - why don't the manufacturers stay away from the complicated and unreliable electronics where they are not needed or make no improvement. Look for a FAULT or ERROR light on the control board - and maybe an error code on fancier ones that you can look up in your manual or on manufacturer's website. There may be a RESET button you can push to tell it to reboot (like rebooting your work or home computer) to try to clear error conditions. Sometimes on initial startup after a long time unused the computers accumulate random error codes from dust or power surges or power flickers or whatever and need to be rebooted to work right.

if none of the above helped, then you need a Heating and A/C technician - and might consider having it cleaned too if it has not been cleaned this season.

Answered 5 years ago by LCD


Hot water on but the gas home heater pilot noton

Answered 4 years ago by bussing57

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