Furnace problem

[leftybj]

My furnace worked fine last Thanksgiving. Made a little trip this week and it got down into the 30's. Turned on the furnace and here is what happened:

Blower turned on,
I heard the burner ignite,
ran for a little while,
burner and blower stopped at the same time,
few seconds later the blower came on,
burner restarted,
ran a little while and the cycle repeated,

the amount of run time was not the same it varied from a few minutes to a few seconds,

After a several cycles I waited for the burner and blower to stop and then switched the unit off at the thermostat. The blower then came on to cool the heat exchanger and then turned off.

Any ideas?

[beazleybub]

Some newer furnaces use what's called a flame sensor. This is in place to keep the furnace from feeding gas to it in the event the flame goes out. The sensor is extremely sensitive and can "foul" with carbon deposits.

They are easy to repair. All you have to do is remove the sensor and take some 600 grit sandpaper to the end of it and lightly sand off any built up carbon and reinstall it.

[jpbuch9309]

Check the air intake for obstructions

[leftybj]

Thanks for all the replies. Turns out that the control circuit board is defective. I checked connections, voltage, air flow blockages, etc. While I had the outside cover off to check connections, there was a troubleshooting chart for the diagnostic LED on the circuit board. I turned the unit on, observed the LED during the fault condition and communicated the results to Camping World where we bought the 5er. They are going to order a new board based on my word and will install it the next time I am in the area, as they are 100 miles away. Looks like we are on the road to recovery. It helps to be thorough in your data gathering to gain credibility with the dealer to resolve issues over the phone instead of travelling to their location each time. Thanks again for the ideas that helped get me to the source of the problem.

[lee_worsdell]

I had to reset my limit switch do to no air flow. My ducts were squashed almost shut. Had to revamp my plenum so I could get better air flow. Cheap little card board boxes they use with 3 4inch pipes. Works 100percent better now

[2oldman]

time2roll wrote:
+1 for 12v power issue. Check fuses and wire connections.

bad battery. Very common.

[Old-Biscuit]

Most common problem with Fan shutting down at same time as burner is the 'time delay relay' being faulty (or blower circuit on newer circuit boards.


Also could be 'high temp limit switch' ......either because it is faulty OR most likely due to obstruction in airflow to/from furnace
Something blocking/obstructing RETURN air to furnace
OR
Furnace discharge blocked/obstructed....too many floor registers closed/blocked or duct work blocked (mouse nest/crushed duct)

Due to airflow issue....high limit switch shuts down firing but fan should still run.

Could be issue with BOTH
Easiest method..clear any obstructions and clean up connections on circuit board then fire it off again and check operation

[time2roll]

+1 for 12v power issue. Check fuses and wire connections.
Verify voltage at the furnace during the event and this may not be exactly easy.

[leftybj]

I will get the furnace info as soon as the rain stops and post it. Thanks

[K_Charles]

Agree with loosing 12 volt power, fan and burner should never shut off at the same time.

[DutchmenSport]

Sounds like you are low on propane, or low pressure on your propane. The furnace is attempting to fire and will burn for a few seconds and then turns off. It will repeat a couple more times until it finally shuts down. Move the thermostat back and forth and it will attempt to kick on again. It may for a few seconds and then shut down. Every time that's happened to me, it's because my propane tank just ran out. But, low pressure because of a clogged regulator, could cause the furnace to do the same thing.

I have found that the stove top burners will still make a flame when my furnace will not kick on because of low pressure or propane tank almost completely empty, but still enough "umph" the stove top will lite.

[jetcare]

If the burner and the blower motor are stopping at the same time, it appears you are loosing the 12 volts to the furnace. The blower motor should never stop during the burn cycle. Please post the model of your furnace so we can look at your specific wiring diagram and give you some more advice. Wiggle the wire connections at the furnace and see if you can duplicate this motor stopping problem during the initial start cycle.

[janechucknicode]

Forget fuel?:S Happened to me x many times.

[lj2654]

use a wire brush and gently clean the area by the igniter and also any flakes of corrosion and then try to light it.

[wkamper]

One of the common things that I have found is the connection to the ignitor is corroded. It is good enough for it to ignite the gas but, not good enough to get the burn signal to the board. Try removing the connector from the ignitor and then reinstall it and wiggle it around a bit. If that doesn't fix it, pull the board and have it checked at an RV repair facility.
Good Luck