furnace problem - 85 Komfort T Class


I have an 85 Komfort T Class with a furnace problem. The furnace seems to work fine but after a few on-off cycles, the heat doesn't kick on and hence the fan just continues to blow cold air.

I've checked the thermostat which seems to work properly and is sending signals to the heater. However, I don't understand why the furnace ignites most of the time, but not all the time.

Help. I'm cold in the desert!!


C Nash

Senior Member
furnace problem - 85 Komfort T Class

Him Dean and welcome to the forum. The furnace should have a heat chamber switch that keeps the blower on after the furnace goes off. Might ck it to see if it is working properly.
furnace problem - 85 Komfort T Class

Hello Dean-o,

I had a 93 trailer (Salem) that when the DC voltage dropped below 10.7 (at the thermostat controls) it would no longer ignite. After a few lights during cold nights it would no longer ignite and just blow air. I had replaced thermostats etc before finding this out in some very fine print. So, to test this I bumped the heat up with full charges several times and it seemed to always light. However, if you are hooked to power and have a constant charge to the batteries this may not be your problem. (unless you are getting a voltage drop before it gets to the thermostat...)

That would be my best guess from your desription.

Good luck!!!!


Senior Member
furnace problem - 85 Komfort T Class


The problem may depend upon just how you are using the furnace. If you are operating on the battery then the problem is very likely one of low voltage. Your RV battery has about 13.5V when fully charged and that voltage slowly falls as the battery discharges. That is normal and the time it takes to fall varies with the battery design and the age of the battery. Your furnace is one of the most demanding loads that your battery supplies. It is not unusual for a battery to be discharged enough by the furnace in one night for the low voltage to cause a problem like you are having.

A DC powered motor, like in your furnace, turns faster at a high voltage and as the voltage falls, the blower turns more slowly and thus moves less air. All RV furnaces use one blower motor that has two sets of blower blades, one to supply the combustion air from outside, and one to move the air through the RV and thus cool the furnace heat exchanger. Those furnaces also have what is called a "sail switch" in the air path that must close for the gas valve to open and thus for the fire to ignite and heat the furnace and the interior. As the battery discharges and the voltage falls, the blower will turn more slowly and at some point it will not close the sail switch and thus it will do exactly what you describe. When the battery voltage has fallen to some point between 11V and 10.5V the sail switch will not close.

Of course, if you are connected to shore power, this should not be the case.
furnace problem - 85 Komfort T Class

Your problem could be one of a few. The most common in your case is that the circuit board is intermittent. Which means its going bad slowly instead of all at once. If this is the case, Replace it with a Dinosuar Electronics board (Model# UIB-L). You can get one cheap @ www.rvmobile.com . It could also be your limit switch. But this usually is accompanied by several light cycles without the fan cutting off. If you listen carefully you will hear them.

However from what you are saying I would be more inclined to remove the board and have it tested. Make sure that they test it multiple times to check for intermittency.