Propane heater not working

[jimsreyes]

I have a 2006 Fleetwood Excursion. My LP-gas heater in the back bedroom went out, meaning it no longer heats. I noticed that the igniter was trying to light it, with no success. And now it seems it doesn't even try to light it. Any suggestions?

[wolfe10]

Jim,

Here is the lighting sequence-- please let us know at what point it fails.

1. The furnace has 12+ VDC to it (check with digital voltmeter at outside access to the furnace. Many models have a fuse on the control board as well as in your 12 VDC fuse box.

2. When the thermostat tells the heater to light, the control board turns on the fan. IF, repeat IF there is adequate air flow to close the sail switch, the control board then opens the gas valve and turns on the igniter. If however, something is blocking the air return or the ducts are kinked, vents closed, etc, the sail switch does not close and the control board does NOT turn on the gas or igniter-- since it knows with inadequate air flow it could cause a fire hazard.

3. In less than one minute (depends on brand and model) the thermocouple must signal the control board that indeed there is a flame burning, or it turns off the propane.

4. The furnace continues to run until the thermostat signals that the set temperature has been reached (or one of the above safety cut-offs takes over).

Brett

[jimsreyes]

Jim,

Here is the lighting sequence-- please let us know at what point it fails.

1. The furnace has 12+ VDC to it (check with digital voltmeter at outside access to the furnace. Many models have a fuse on the control board as well as in your 12 VDC fuse box.

2. When the thermostat tells the heater to light, the control board turns on the fan. IF, repeat IF there is adequate air flow to close the sail switch, the control board then opens the gas valve and turns on the igniter. If however, something is blocking the air return or the ducts are kinked, vents closed, etc, the sail switch does not close and the control board does NOT turn on the gas or igniter-- since it knows with inadequate air flow it could cause a fire hazard.

3. In less than one minute (depends on brand and model) the thermocouple must signal the control board that indeed there is a flame burning, or it turns off the propane.

4. The furnace continues to run until the thermostat signals that the set temperature has been reached (or one of the above safety cut-offs takes over).

Brett

Thanks for your help! I don't know what happened but I tried to turn it on again and guess what?! Back heater is working! Just a mystery I guess!

[chucknewman]

Jim,

In most cases when I've seen the intermittent operation you describe, it is either low voltage or a sticky sail switch that Brett described.

Most 12 vdc relays, which your furnace will have 2 or 3, are at their lower operational limits between 11.0 and 11.5 vdc. When you have around 11.0 volts some relays will not work, others work intermittently. Either condition will not allow the furnace to function properly. Then you start the gen or plug in to the post and the furnace miraculously works because the battery charger has increased the DC voltage to normal.

The actual switch activated by the wind sail (usually a light piece of composite or sheet metal) can go bad, but many times the sail gets sluggish due to accumulated airborne debris that builds up on the sail's shaft. It can be cleaned and lubricated with dry silicone lubricant. When the furnace is off and power removed of course (just pull the appropriate fuse).

Larger home and commercial furnaces use a vacuum switch to sense combustion air flow. The vacuum created by flowing air closes the switch, and signals the printed circuit board to open the gas solenoid and activate the striker. The vacuum hose can get debris in it and block the vacuum, but I don't think and RV furnaces use that setup.

Unfortunately, if you don't find and fix the problem this summer, it will revisit you next winter.