my gas furnace will not produce a flame the ignitor willheat up and glo but wont light the flame?
- RolomaticLv 612 months ago
Check the plenum and burner manifold overheat rollout switches, some are manual reset type where you push in the red plastic reset button. If one of them goes bad, you will get no voltage to the gas valve. If this is a 85% or better efficiency model with an *inducer fan, there is a vacuum dash pot safety switch on the inducer fan housing that also often goes bad. With a volt meter, follow the gas valve power back from the valve to find the safety interlock switch that has 24VAC on the input side. If the valve has 24VAC, smack it with a wrench when you see the igniter glow and 24VAC hit the valve at startup. Sometimes the gas solenoid valve can get stuck closed when it's not used for many months in a humid environment, then a quick whack from a wrench will often get them to open and operate properly again.
The gas valve power may go through several safety switches before it gets to the gas valve solenoid from the control board. You will easily see the wire that loops through the safety sensors and then runs down to energize the gas valve. You can start with the safety switch closest to the main wires from the control board and work out that way too. Ether way, that 24VAC from the control board feeds through all the safety switches in series to the gas valve. If this info is total svengali to you, hire a qualified technician to sort it out and get it working. In most cases it's a $10 rollout limit or a $25 inducer fan dash pot switch that fails.
I keep a 3 inch wire with female spade connectors in my tool pouch for this reason, to bypass for testing.
I'm not saying to bypass a safety switch, sometimes it's necessary to prevent pipes from freezing til Mon.
*If your inducer fan has died, that would be why per the inducer vacuum dash pot safety interlock switch.
Operation is as follows:
1) If you have an inducer fan, it will start and close the inducer dash pot switch. (or skip without inducer)
2) The electric glow igniter will warm up for 10-20 seconds.
3) The gas valve will kick on and run for 20 seconds waiting for the flame sensor input to stay on.
Pay attention to what it's doing, your issue is pre burn stage so it's in the 24V safety interlock switches.
The furnace chassis is ground on the gas valve so chase the 24V on a volt meter back from the gas valve.
All the other answers here are worthless as help, we all know you can pay more for a pro then free advice.
Beyond that, you would have to post the manufacture and model of the furnace air handler unit to lookup.
- STEPHENLv 71 year ago
Check that the gas is turned on at the mains tap.
Beyond that get someone that is qualified and licensed to look at it.
Playing around with gas when you don't know what you're doing (and if you knew what you were doing you wouldn't be asking this question) could result in there being a big hole in the ground where your house used to be.
- Mr. InterestingLv 71 year ago
The gas is not coming on. There is something keeping it from happening.
First, you need to turn off the gas to the furnace. Then, remove the front panel to find the ignitor or ignition sensor. This is typically located near the burners.
If the sensor or ignitor is dirty, it will need to be cleaned. Remove it with a screwdriver and clean it while being careful not to break it.
When you are finished, replace it exactly the way you found it. Put the front panel back on, turn on the gas, and then turn the furnace back on.
Turn up the temperature on your thermostat to see if your furnace will now fire up.
- MarkoLv 61 year ago
See if there are cracks in the ignitor. You can unplug it and look at it.
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- Anonymous1 year ago
Gas valve is suspect. Firstly replace the flame failure device. If that doesn't work you need a new gas valve.
- PearlLv 71 year ago
maybe you should have someone check it out