RV’s furnace blows warm air only. What should I check?

Dear Dave,
My RV’s furnace is blowing warm air, not hot air like it used to. The propane tank is full; stove, fridge, water heater work fine. Battery voltage is 13.2. When turned on, the fan starts and a few seconds later I can hear the burner ignite. What should I check first? Thanks. —Rick, 2010 Thor Four Winds Siesta

Dear Rick,
From what I can tell in the 2010 Siesta brochure, all models came with a 25,000 BTU furnace. It looks to be forced air with corrugated ducts running through cabinetry to the vents.

These ducts are connected to the main furnace assembly and can often get loose, obstructed or kinked. If they are obstructed or kinked, typically that would create a restricted airflow and either trip the temperature sensor or the sail switch and shut the unit down. Warm air would indicate a hose got disconnected and warm air is blowing in other directions. I would suggest that you check the hoses at the main furnace and in the cabinetry as well as at the vent.

If these are all connected, the next step would be to get an airflow meter called an anemometer to get actual airflow and temperature. Here is one available on Amazon.

I would check the temperature at a vent and then at the furnace itself by removing one of the hoses. This will tell you actual data regarding what is coming out of the unit.

Verify operation of the furnace

The next step would be to verify proper operation of the furnace. It is possible that the unit is igniting, the fan is running, but then it is shutting off due to the sail switch not lifting high enough or the temperature sensor. The sail switch can get dirty and is too heavy to stay up and just needs to be cleaned.

If there is a blockage in the hoses, or a vent is covered, the sail switch can fall down or the temperature gets too hot and the temperature switch shuts the unit down. In this case, the fan keeps running but there is no ignition so there is only the residual heat from the burner assembly when it was running.

If all this checks out, it could be the burner assembly is getting clogged with soot, which limits the flame and output. This requires removal of the furnace and taking the cover off the burner plate.

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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