I need help

[Lizy]

Hi I have a 1980 big foot trailer the fa7912 hydro flame furnace is given me trouble.It lights goes one full cycle then the pilot light goes out help what could it be.

[reetired]

Ummm spiders?

Is there an adjustment....like lighters have?

[Darwin Maring]

If there is an inspection plate, look to see if there is any water inside the combustion chamber.

[Bob Miller]

That problem is typical of a defective thermocouple or flame safety valve. Happens all the time with water heaters.

if you are lighting it the first time with a match, be sure that the thermocouple is in the pilot flame.

[Francesca Knowles]

Originally Posted by Lizy

Hi I have a 1980 big foot trailer the fa7912 hydro flame furnace is given me trouble.It lights goes one full cycle then the pilot light goes out help what could it be.

I'm not exactly sure what you mean by "one full cycle", but:

Do you have the owner's manual? If not, here's a link to the correct manual.

Do check out and adhere to starting sequences described therein. That furnace is most particular and will not function unless they're strictly followed.

Good luck!

[Bob Miller]

It you manually light a pilot with a match, the match can heat the thermocouple causing the valve to latch when turned to run. But, when the furnace cycles OFF, either if there is no working pilot or it isn't impinging the thermocouple, the pilot safety gas valve will release.

This is a reason why match light water heaters do a single cycle and then don't relight.

[Lizy]

What I mean by full cycle is I set temp on the thermostat it gets to that temp as it is cooling down the pilot light goes out.

[Bob Miller]

What may be happening is that the furnace flame keeps the thermocouple hot, but when it turns off the pilot is not hitting the thermocouple enough and it releases the safety valve, shutting off everything. Check to see if the thermocouple probe is in the center of the pilot flame.

[Bob Miller]

I looked at the manual that Francesca posted above and it appears that furnace is available with and without a pilot. Does yours require pushing the igniter button to light or is it automatic. Is the last letter of the model number a D or a P?

[Francesca Knowles]

Originally Posted by Lizy

What I mean by full cycle is I set temp on the thermostat it gets to that temp as it is cooling down the pilot light goes out.

Found another source that gives general troubleshooting tips covering many furnaces including this one. Here are the possible causes they list for the symptom you describe:

PILOT FAILS TO IGNITE OR STAY LIT
Plugged pilot orifice ---------Clean or replace pilot orifice.
Electrode out of adjustment ---------Adjust electrode to furnace’s specifications.
Pilot tube defective -------Replace tube.
Piezo sparker defective ---------------Replace sparker
Defective thermocouple -------------Replace thermocouple.
Defective valve--------------------Replace valve.
Vent kit not sealed ----Seal vent where it meets with the furnace.*
MICA window missing------------Replace MICA
Combustion air hose plugged or collapsed-----Replace combustion hose
Water in propane ----------Add alcohol to the propane bottles.*
Burner plate gasket or --------Replace gaskets
pilot gasket not sealed

[Lizy]

It has pushing igniter model is fa -7912 PF

[papa-t]

Ummm also check for other critters like mud daubers. Mine on another unit would light and then go out. The tube was full of mud daubers. Just a suggestion.

[Donna D.]

Spiders are the worst. You can't see the web. Get a long pipe cleaner and clean. Try the cheap stuff first!

[Carol H]

All it takes is one tiny spender or a little web for the pilot to go out.

[Donna D.]

Spider cause all kinds of problems with BBQs and always at the worst time...

[RogerDat]

If this model has low oxygen shut off it probably depends on pilot flame burning high enough to maintain the thermocouple temperature. Safety feature as low oxygen would cause less height in pilot flame, so furnace would shut down.

Question: Does the pilot stay lit if the furnace does not cycle? If you light the pilot with the thermostat turned down too low for furnace to come on does the pilot still go out shortly after?

If so one can eliminate anything to do with thermostat cycling the furnace.

Might look at venting if the furnace lacks sufficient venting and is using up the oxegen when it runs it could (and should) cause the pilot to have a smaller flame so it can't heat the thermocouple.

Might try cleaning the thermocouple end where pilot heat is applied and maybe the pilot burner itself as low cost general maintenance.

[stevebaz]

How old is the pressure regulator on your propane tanks? low propane pressure can cause this issue.