Pilot (standing) and Burner will not light. Old gas forced air furnace

[ajrn]

It stayed warm enough this fall, that I didn't even try to light the furnace on my currently un-occupied rental property until earlier this week.  Yup, it's about 50F inside, but again, with no one inside, it was warm 'enough.'

It has a "Floral City" Flo-co furnace, built in Monroe, Michigan.. I'd assume it was probably put in in the '60's....  It's a very simple-- single burner, standing pilot, forced air furnace. It's never needed a damn thing in the 15+ years I've owned the house. When I first bought it, I had a friend (now deceased from asbestosis) who was an hvac guy come "check" it.. He replaced the thermocouple, left me a spare, and showed me how to replace it.. Oiled the blower motor, showing me that, showed me how to replace the belts, clean the burner orifice and "adjust" the burner. 

So-- when I tried to light it, and the pilot wouldn't stay lit.. I thought-- well, maybe that thermocouple has finally died..  I grabbed the spare he'd left me..  No dice..  I've considered buying a "new" one-- that is, one that was "just made" but-- I doubt that's my issue (or am I wrong??)..

I do have voltage at the transformer.. 

My concern that the Honeywell gas "valve" has died.. No, I haven't gotten part numbers off it. (but would if this would help someone-- again, the valve is realistically 20+ years old..  I know the transformer was built "by Honeywell in MN, USA.."  That should tell ya it's not "new..." (sadly..)

Removing the gas valve doesn't look difficult in the least.. There's a pipe union OUTSIDE the furnace cabinent.. That removed, would probably allow me to remove the entire burner assembly and the gas valve with maybe a half dozen supporting screws, then just undoing the pipe leading to the control, and the burner, and replacing the valve-- obviously paying attention to polarity on the wiring, as I did..  New thermocouple-- replace the plumbing (using YELLOW teflon tape-- which I already have) check for leaks with soapy water-- done, right??  I'd be willing to listen to anyone who suggested I cut the gas to the house, and replaced the main gas and pilot gas valves, while I have it "apart.."

I can take pictures, and try to find model numbers, if it helps someone answer the question.. 

Assuming I can find someone to sell me the parts (I'm not a "contractor..") is there any reason I couldn't replace this?? 

BTW-- just because I'm going to get a "new" one anyway-- I do plan to try yet another thermocouple, just in case the one in the package, had failed without use..  Is there a way to test them, using a multimeter-- and maybe a match??

Standing by, ready to absorb knowledge..

AJ RN

 

[RegUS_PatOff]

Is the Thermocouple in the Pilot Flame "nicely" ?

and you held the "Pilot Button" for 30 seconds or more ?

 

 

[ajrn]

Yes to both.. (I've lit it probably 20 times in the time period.. Sometimes I've shut if off "too soon" in the spring..

[RegUS_PatOff]

A good Furnace Thermocouple may only put out 20 to 30 millivolts.

You could try using the flame from a lighter.

 

 

[ACtechGUY]

Your pilot flame should be a lovely shade of blue. If it is yellow in the least , there may not be enough heat to generate the 20 or so millivolts required to keep the pilot soloniod energized. If you do have a yellow flame , disconnect the pilot tube at the gas valve and blow it out with compressed air or something similar. This will clear an oxide that builds up on the pilot orifice.

To test a thermocouple.You need a Multi meter set to dc volts in the millivolt range. Unscrew thermocouple from gas valve.(This test requires the use of aligator test leads or 2 people , one to hold the leads and the other to light and hold the pilot button) One lead on the outer copper and the other on the silver tab on the end that screws into the valve. Thermocouple should be encased in the pilot flame. With a good flame (sorry not a match or aim-n-flame) you will see the voltage climb over 20- 30 seconds to max out around 30 mv. You need a minimum of 18-20mv to keep a gas valve pilot open.

[ajrn]

I'm going to heat up the old thermocouple, and test it, (to see if it was making the required 20-30mv..)  I do have a meter that will read that. I'll use a propane torch to warm it up-- so there won't be a question there. 

I knew they made a small amount of "energy" but I wouldn't have known how much without asking here..

My pilot flame is a nice pretty blue-- but I do like the idea of blowing it out with compressed air..  Have an air compressor that would LOVE to help me with that..

If not, am I correct to assume it is the valve itself that's failed, as the transformer is making electricity??

 

BTW-- thanks to those who've "helped" already.. 

[ACtechGUY]

The transformer really has nothing to do do with the pilot flame. If you had a working thermocouple and an ok gas valve , you would not need any a/c power to keep the flame going.

The tiny voltage generated by the thermocouple is what keeps the gas flowing to the pilot flame.

There is also one more possible problem. That is assuming the thermocouple and gas valve are ok.

The thermocouple may have a safety switch in the circuit. If you see wires or connectors at the location where the thermocouple screws in you may have an open safety switch in the pilot circuit. Just follow the wires to a Failed or tripped over temp switch and jump out switch(TEMPORARILY) . Try to light pilot again.

[applianceman18007260692]

Check the gas valve's solenoid. If it reads open it is bad.

[ajrn]

Well I'm running...

Tested the "replacement" thermocouple with a "blue tip" wrench (propane torch) that night.. I was AMAZED at how little differences in placement made a HUGE difference on output.

I used the multimeter to "place" the thermocouple-- that is using it to sense where I was getting the "best" voltage, then backing away a little-- since it was reading OVER 31mv.. I found a spot where it reads a very consistent 27.1mv, and bolted it it..

I did test the gas valve for continuity.. It was okay..

Said a prayer, and off she went..

Couldn't have been happier, with the sub-freeze we've been at the last few days..

Thanks to all, God bless you, Merry gentlemen-- and Merry Christmas!

Anthony

[RegUS_PatOff]

[user=25079]ajrn[/user] wrote:

... Couldn't have been happier, with the sub-freeze we've been at the last few days..

:brrr:

Wisconsin here ..

[ACtechGUY]

It must just suck to live up there sometimes. It was 70 degrees here yesterday.:doublefinger:

Glad to be of help.

[ajrn]

I would take cold ANY day..

Us fat folk can only take so much off-- we can always put more on.