Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Thanks for the opportunity to help!
You know anything about error #34?
Yes, it is an ignition proving fault. Are burners lighting at all?
I don't think so. The ignitor lights, but I don't think gas is flowing. I cleaned the sensor, but no change in amps across it when ignitor lights up. I'm assuming no flame.
So burners do not light at all, even if only briefly?
Have you checked for gas flow to the furnace?
Gas line also goes to hot water heaters and those are working fine.
I would start by cracking a union close to the furnace and make sure it's getting gas. We can't assume anything.
Ok, that will take some time. Let's assume gas is flowing. How do I check the gas switch mechanism that the gas flows into. It has an on/off switch.
Make sure it has gas and that the on-off knob on top of the gas valve is in the "on" position. If everything looks good there, next step is to check for voltage at the 2 gas valve terminals around the time ignitor comes on
We should have 24 volts AC
Ok, if no 24ac then what? If we do have volts, then what?
If you have voltage and good gas flow, then you have a bad gas valve. If no 24 volts anytime around the time ignitor comes on would signal a bad control board
That's pretty much ends the troubleshooting I would assume. Is gas valve easy to replace? Just remove top & bottom connections and wires?
Yes, fairly easy.
I don't like working with gas. When I "crack" a union, what do I need to seal it back up?
You just take 2 adjustable wrenches and turn the 2 halves just enough to hear if gas is coming out. Then immediately tighten them back up. You don't even need to take it totally apart.
Unions are self sealing
I'm not sure I have a union. I've got a ball valve. Out of that comes a flexible gas tube that runs into the unit and connects directly to gas valve. Can I just close ball valve and loosen connection to gas valve?
Yes, you can do that and then briefly open the valve.
Is there a special sealant, puddy I need to put in treads when reconnecting?
Yes, if and when you install a new gas valve, use any standard pipe "dope"
It's just to lubricate the threads
Ok, but I don't need it if I'm just loosing connection & listening for gas?
Most home improvement stores will help you with selecting a pipe dope. No, you don't need just to loosen and listen for gas
In a nutshell, if burners don't light I've got
1. gas blockage/no gas
2. bad gas valve
3. bad control board
Anything else that I need to check?
Absolutely correct! And we determine that by whther or not there is 24 volts AC to the valve or not
got it. Thanks for your info. I'll go work on it and see. What do I need to do for you?
Yes, good luck! Thank you for using Just Answer and please don't forget to rate my service. (Bonuses are always appreciated). Feel free to post back with any additional questions.
Tim, are you there?
Cracked union above gas valve. Gas was flowing.
Ran unit. At rest, valve was reading 15V ac. When ignitor lit, valve read 28v ac. Assume bad gas valve.
It's a white-rogers, but no marking on it. How do I know part #?
Yes, if gas to valve and valve receives voltage and doesn't let gas come through, that would be a bad gas valve
I took it off, btw. There is a gas manifold attached to bottom. Not sure how to take that off without bending it.
I called local supply house. They won't sell to me...said I'd blow up my house.
It should just unscrew from valve
Any idea how to find PN?
If you give me full model number, series number and serial number of furnace, I can locate a part
ok, got to go look. hold, please...
This should be the part you need, part# XXXXX
Ok, thanks again for the help.