Need some help diagnosing & fixing gas furnace problem. - Contractor Talk - Professional Construction and Remodeling Forum

whiterabbitva · 11-13-2008, 06:54 PM

The unit is my mother's & I was trying to save her the money a service call would cost her, so before I tell her to call a HVAC company I thought I'd see if any of y'all could help me out.

It's a 24 year old Bryant gas furnace, Model #394GAW036100. Downflow vented (? i think that's how to describe it), electric arc ignited pilot.

The problem: It stopped firing up the burners on monday. The thermostat would call for heat, it would start the cycle by igniting the pilot, but it wouldn't fire up the burners and wouldn't stop arcing the igniter even after the pilot was on.

Sooooooo... this is what I've done so far.
I checked all the safeties to ensure they were functional and closed by testing continuity through each one.
I checked the whole safety circuit itself and read 24v to ground and 0v across the two control board terminals the circuit is run between.
I bypassed the safety circuit itself by disconnecting the leads and jumpering the contacts on the board.
I checked for power at the gas valve and read 24v between the pilot valve terminal and ground, but nothing on the main gas valve terminal.
I jumpered 24v from the pilot terminal to the main gas valve terminal temproarily and it opened and the burners lit.
The pilot assembly includes a flame sensor safety, so I replaced the entire assembly thinking that if it didn't see the pilot it wouldn't let the main valve open.

Problem was exactly the same.

I double checked everything I had checked previously and got the same results. So I replaced the control board thinking that it might not be reading the signal from the safety pilot.
No change.
As far as I can tell I've checked or replaced every safety component including fuses and fusible links. I'm at a loss as to what to do.

Any suggestions as to what I've missed?

rbsremodeling · 11-13-2008, 06:58 PM

Quote:

Originally Posted by whiterabbitva

The unit is my mother's & I was trying to save her the money a service call would cost her, so before I tell her to call a HVAC company I thought I'd see if any of y'all could help me out.

It's a 24 year old Bryant gas furnace, Model #394GAW036100. Downflow vented (? i think that's how to describe it), electric arc ignited pilot.

The problem: It stopped firing up the burners on monday. The thermostat would call for heat, it would start the cycle by igniting the pilot, but it wouldn't fire up the burners and wouldn't stop arcing the igniter even after the pilot was on.

Sooooooo... this is what I've done so far.
I checked all the safeties to ensure they were functional and closed by testing continuity through each one.
I checked the whole safety circuit itself and read 24v to ground and 0v across the two control board terminals the circuit is run between.
I bypassed the safety circuit itself by disconnecting the leads and jumpering the contacts on the board.
I checked for power at the gas valve and read 24v between the pilot valve terminal and ground, but nothing on the main gas valve terminal.
I jumpered 24v from the pilot terminal to the main gas valve terminal temproarily and it opened and the burners lit.
The pilot assembly includes a flame sensor safety, so I replaced the entire assembly thinking that if it didn't see the pilot it wouldn't let the main valve open.

Problem was exactly the same.

I double checked everything I had checked previously and got the same results. So I replaced the control board thinking that it might not be reading the signal from the safety pilot.
No change.
As far as I can tell I've checked or replaced every safety component including fuses and fusible links. I'm at a loss as to what to do.

Any suggestions as to what I've missed?

Welcome to contractor talk. My diagnostic would be to tell your mom she needs to tell her cheap son to call an HVAC contractor out and change out the 24 year old unit that she got all her moneys worth out of.

By the way Welcome to the site

whiterabbitva · 11-13-2008, 09:10 PM

Thanks for your concern about my thriftiness, however I won't belabor the reasons for trying to save an older woman on a fixed income, whom I already help support, a little money. She is replacing the unit next year when she adds a/c and does away with her horribly inefficient and ugly window units, however I'd like to get her thru the winter at least.

Thanks for the welcome, though.

nhmaster3015 · 11-13-2008, 09:15 PM

With any luck, your tinkering around with something you know nothing about will result in either fire, explosion or Monoxide poisioning or some combination of the three, ending the poor womans life and naturally any concerns she may have had. If you are so worried over her fixed income, why not pay the service guy yourself? After all the woman did spend thousands of dollars raising your miserable cheap ass.

rbsremodeling · 11-13-2008, 09:16 PM

So you rather play with gas, electric, illegally than pony the money up for a service tech at your moms house??

Your welcome. Hope you enjoy the site

MALCO.New.York · 11-13-2008, 09:20 PM

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mo-flo · 11-13-2008, 09:49 PM

might as well change valve while you are at it......sounds like you've changed everything else already.How are you getting parts anyway?Be careful what you are doing,you could end up with more problems than when you started time you call a service man.

whiterabbitva · 11-14-2008, 11:15 AM

I wasn't going to change the valve myself, if it needed to be. I wouldn't do anything I wasn't entriely comfortable doing in the first place.
I am fully capable of testing and replacing electrical components in any system. Contrary to apparent popular belief I wasn't messing with anything that could compromise the safety of the unit itself. Unless you can show how replacing a sensor and control board with OEM factory parts would do so.
Unless of course the nonexistent gas coming out of the MGV spontaneously combusted.
As for the parts question, I got them locally from a distributor, but you do realize that everything not state or federally regulated (and sometimes even then) is easily available online anyway. And thanks, I am being careful.
Also I don't think anyone has the time for me to lay out all the stuff I've done over the years to pay my mom back for all she did for me, so get off the high horse there. Besides, I'm paying for the parts, taking my time in the evening and will pay the service tech. When you try and save money you don't always end up doing it, but you do enough to make it worth the attempt.
I mean I did only ask for a simple "Hey you missed "X" completely" or "No one can help you, call the service tech." Not a diatribe on my abilities (or lack thereof) or my relationship with my mom, neither of which you know anything about.

nhmaster3015 · 11-14-2008, 04:22 PM

What we do know is that you are just another guy trying to justify his actions to guys that could care less what you think you can do. You don't have license to service gas equipment and that's all that matters. Note how nobody has offered any advice at all even though several of us know the answer to your problem.

jhvac · 11-14-2008, 10:46 PM

I installed a goodman 90% furnace and it will only run with the burner door off

nhmaster3015 · 11-15-2008, 08:13 AM

That's a shame

I have faith in you though. You'll figger it out

whiterabbitva · 11-15-2008, 09:34 AM

Whatever. Figured it out, finally... myself. I don't need to justify anything to any ignorant, condescending jerks whose opinion i could give two sh**s about, but whose technical knowledge I might have respected. Had the response been "You shouldn't mess with it, call a tech because...", I might have done just that. That's how normal people respond to a question. But to instantly deride someone because you don't know how to be civilized or professional is just sad. Not to mention last time I checked, in VA I can, as an owners agent, work without permit on any wiring that operates on less than 50V unless it's in a fire alarm or suppresion system. And if you KNOW any differently, why not simply state that and drop the middle school type name calling.

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**AtlanticWBConst** · 11-15-2008, 10:13 AM

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