Home Furnace: Failure to light, fan safety switch?

[bmbutch]

Furnace Wouldn't Light:
1) Cleaned Ignitor.
2) Cleaned Flame Sensor.
Watched what happened: Purge, Blower Start, Ignitor Activates, gas valve clicks, nothing happens.
Gas Water Heater is working fine.
3) Tried tapping on valve after click, nothing
4) Called service
They traced it back to low voltage to gas valve, traced back to two safety switches on fan. He jumped them out, system fired up. Pulled jumper off & it shut down.
Said he wanted to confirm some things, then came back in & said it's working fine. Admitted he can't exactly explain why they were tripped, why they wouldn't reset, or why they started working again. Have part numbers for new if needed.

Any opinions of the above, anything I should do next? Seems odd to me, but I know almost nothing about HVAC.

 

[bocefus78]

Paging churchmouse.

 

[ChristianPatriot]

Do those switches have pneumatic tubing coming out of them?

 

[EyeCarry]

Check your fresh air intake/exhaust for a wasp nest. Happened to me one time with similar symptoms. The furnace had sucked the nest all the way back into the furnace causing it to not get enough air. The vacuum side of my blower/vac sucked the nest right out and shredded it through the vacuum's impeller.

 

[bigretic]

Check your fresh air intake/exhaust for a wasp nest. Happened to me one time with similar symptoms. The furnace had sucked the nest all the way back into the furnace causing it to not get enough air. The vacuum side of my blower/vac sucked the nest right out and shredded it through the vacuum's impeller.

yeah, or just leaves even. I've had snow drift around it also and lock out the system.

 

[bmbutch]

Do those switches have pneumatic tubing coming out of them?

Nay

 

[ChristianPatriot]

Well it won’t even try to lite unless the airflow switches have made so the fact that’s it’s sparking means that the airflow is ok.

 

[churchmouse]

Furnace make.....how old....plastic or metal exhaust flu.....is there a circuit board on the blower. Whet fan, exhaust or main blower. If it was the exhaust the safety could be weak and needs replaced. It will open if the flu gets to hot. If it is the main blower those should be manual resets. They will trip if the furnace overheats for any reason mainly a dirty filter or a slow/no blower.

These are all unseen guesses at best. It could be something totally different.

 

[churchmouse]

Another double...

 

[possum_128]

Another double...

Check with a mod, they might be able to help.

 

[femurphy77]

Another double...

Check with a mod, they might be able to help.

Nah, he's padding his post count!

 

[bmbutch]

Goodman, 4 years old (house was complete July 2013), dates on unit are Mar 2013. Plastic Flu, & now I show my ignorance, fan is one on top section with circuit board. Bottom section has burners, valve, etc. Tech., said he's not seen safeties on that fan before?

 

[churchmouse]

Goodman, 4 years old (house was complete July 2013), dates on unit are Mar 2013. Plastic Flu, & now I show my ignorance, fan is one on top section with circuit board. Bottom section has burners, valve, etc. Tech., said he's not seen safeties on that fan before?

Tech was a stooge.
Filters clean...etc.

 

[bmbutch]

Tech was a stooge.
Filters clean...etc.

Just changed it during it's no work time. 4" filter, old one wasn't that dirty. Did try turning Furnace on/off a couple times.

 

[churchmouse]

Just changed it during it's no work time. 4" filter, old one wasn't that dirty. Did try turning Furnace on/off a couple times.

If he said the safety on the main blower was tripped most of those are manual resets. He could have well nudged the reset which is dead center on the safety.
If this happens again do not do a hard reset on it as in cycling main power. There is a plastic peep hole in the blower door. If a safety opens it should give you a flash code on the board light. You can see this light through the peep hole. The code will steer you in the general direction of the failure. The reason may have to be discovered.

 

[tmschuller]

Does that model have a test on the circuit board?? If so follow directions on the door. i am following for interest. Had one similar to the issues but it was a blocked drain for the condensate for the burner box. Might check all tubing for the drains

 

[BiscuitsandGravy]

My mothers LP furnace had the same symptoms this pass weekend... Narrowed it down to jumping out a pressure(vacuum) switch on the exhaust fan and it fired up. Used a large paper clip straightened out to poke out what looked like soot in the port the hose attached to on the furnace. Did a manual (via mouth) vac test on the switch with continuity tester and the switch checked out. Re-attached everything and it fired up.

Basic troubleshooting minus actual part failure...

 

[churchmouse]

My mothers LP furnace had the same symptoms this pass weekend... Narrowed it down to jumping out a pressure(vacuum) switch on the exhaust fan and it fired up. Used a large paper clip straightened out to poke out what looked like soot in the port the hose attached to on the furnace. Did a manual (via mouth) vac test on the switch with continuity tester and the switch checked out. Re-attached everything and it fired up.

Basic troubleshooting minus actual part failure...

Bingo.
On the OP's issue the ignition process will not start if the safety's on the flu are open. On the dual pressure safety's one will have to prove as in close in a set time period to prove to the board the exhaust fan is operating. Then the ignition cycle starts.
If there is an open safety in the circuit with the gas valve the symptoms will be a described on some units.
It should throw a code on the board.

 

[bmbutch]

So far it's still working, when it stops working, I'll check the board for sequence of flashes.

Thank You Churchmouse & others, much appreciated.

Amazing how I'm comfortable in house @ 67, but 60 was COLD!

 

[churchmouse]

So far it's still working, when it stops working, I'll check the board for sequence of flashes.

Thank You Churchmouse & others, much appreciated.

Amazing how I'm comfortable in house @ 67, but 60 was COLD!

Mentally, just knowing you had no heat makes you aware.

No worries. Love to help.