Furnace: Troubleshooting RV Furnace Problems

If you’re a new RVer it may help if you have a good idea of how your RV furnace should work.

• Your RV furnace operates on the 12vdc system, You do not have to be plugged into 120v power use it.

• If your thermostat only controls the furnace and has a switch to turn the furnace on/off, switch to ON position. If your thermostat controls the furnace and the air conditioner make sure the switch is set to FURNACE.

• Set thermostat to warm temperature and furnace blower should come on after 15-30 seconds.

• The blower runs for 15-30 seconds then the burner will fire up. It’s normal for burner to cycle on and off.

• When the proper temperature is reached the burner will cut off, the blower will continue to run for a short time.

Some common RV furnace or heater problems can be solved with basic troubleshooting and simple repairs. Keep in mind that any RV furnace repair should be done by a qualified technician.

Pilot Light Won’t light or stay lit.

Make sure the thermocouple is positioned properly in the pilot flame.

Another common problem is a bad regulator at the propane tank. A simple test will indicate if this is the case. Light all the stove burners and look at the color of the flame. The flames should be blue with little or no yellow color. If the flame does not change color then the regulator is probably working. A bad regulator could also cause problems with your hot water heater.

Note: Most modern RV furnaces have a direct spark ignition system that replaces a pilot light.

The fan doesn’t run and no heat. If the fan will not start you should first check that your battery is good and you have 12 volts at the furnace. You could have a tripped circuit breaker or a blown fuse.

If the battery is good and you have electricity to the RV’s heater next check the thermostat.

Remove cover and look for the “anticipator” adjustment. (Note: Some new thermostats do not have an anticipator.) It will be an adjustable control with a sliding contact over a straight bare wire or a bare wire wound about an insulating material. If the fan will not start set the temperature to maximum and then move the anticipator slider while listening for the fan to start. Be sure to wait long enough… it normally takes our furnace 30 seconds for the fan to start once the thermostat sends a signal.

If the fan starts after you move the slider then you have probably found the problem. In this case, you may find a slider position near the original position that will work reliably. If your thermostat anticipator adjustment uses the straight wire design and the wire lies directly on the plastic housing then you should look to see if the wire has sunk into the plastic. This wire produces heat and causes the plastic to melt a little and the wire to sink into the plastic so the slider no longer makes contact. It may be necessary to replace the thermostat.

Fan runs but no heat.

If your furnace fan starts you can assume that the thermostat is working.

Possible problems are insufficient airflow through the furnace a bad propane valve at the furnace or a bad regulator at the propane tank.

A furnace contains an internal sail switch, that senses the airflow. If the airflow is not sufficient then the switch will prevent the furnace from igniting and the fan will run but you will get no heat. A slow motor speed could be caused by a low battery or other low voltage cause such as a bad connection in the wiring.

Low airflow could also be caused by a restriction in the ventilation system. Check to see if any heat registers are closed or blocked. Some furnaces will not tolerate even a partial closure of a heat register.

If you have an electronic ignition check to see if the two contacts are touching or are too far apart. They should be about 1/8 apart.

Condition Solution
No Electrical Power to the furnace   Reconnect or replace the power source
Thermostat defective   Replace thermostat
Thermostat wires are broken or shorted   Replace wire or wires
Circuit breaker defective or tripped   Reset circuit breaker and check amp draw from motor according to furnace’s specifications
Blower relay defective   Replace relay
Wire off motor or relay   Reconnect wire
Bad ground   Clean and secure grounds
Blower motor defective   Replace motor
Low voltage   Correct Power Supply
Gas pressure incorrect   Set pressure to a minimum of “11” W.C. with all appliances running. Replace regulator if not obtainable.
Furnace ground wires not secure   Clean and secure grounds
Air intake restricted   Clean air intake
Motor running slow   Correct polarity
Combustion air wheel loose   Check voltage, if 12 VDC while running, replace the motor
Exhaust blocked   Clean exhaust
Sail switch defective   Reposition and tighten
Limit switch defective   Replace switch
The edge connector on circuit board dirty   Clean with a pencil eraser
Circuit board defective   Clean plug contacts. If still defective, replace (check onboard tester when possible)
Gas valve defective   Replace the valve or valve coil
Main burner orifice blocked   Clean main burner orifice or replace
High tension lead wire defective   Replace wire
Electrode out of adjustment   Adjust electrode (don’t crack the porcelain)
Electrode defective or cracked   Replace electrode
Obstructed burner head   Clean burner head
Low gas pressure   Set pressure to a minimum of “11” W.C. with all appliances running. Replace regulator if not obtainable
Exhaust blocked   Clean exhaust
Combustion air loose   Reposition wheel and tighten
Electrodes out of adjustment   Adjust electrodes to proper specs
Electrode defective   Replace electrode
Circuit board defective   Clean plug contacts. If still defective, replace.
Flame sensor wire between electrode and circuit board defective   Replace wire
Air leakage at gaskets   Replace gasket
Defective heat exchanger   Replace heat exchanger
SOOTING (caused by lazy yellow flame)
Low gas pressure   Set pressure to a minimum of “11” W.C. with all appliances running. Replace regulator if not obtainable
Low voltage   Correct power supply
Air leakage at gaskets   Replace gaskets
Combustion wheel installed backward   Reposition wheel and tighten
Blockage in the heat exchanger or burner head   Clean or replace
Faulty motor   Replace motor
Defective thermostat   Replace thermostat
Shorted thermostat leads   Replace wiring
Defective relay   Replace relay
Furnace over fired   Set gas pressure to a minimum of “11” W.C. with all appliances running. Replace regulator if not obtainable. Also, check the main burner orifice, it must comply with the furnace’s specifications.
Restricted return air supply   Make sure return air meets furnace’s minimum requirements
Restricted or insufficient discharge ducting   A) Ducting must meet minimum specifications
    B) No excess ducting or unnecessary bends
    C) All closeable registers must be fully open and unrestricted
Defective limit switch   Replace limit switch
Wired wrong   Correct wiring
Faulty relay   Replace relay
Motor mount loose   Tighten the motor mounting bracket
Damaged blower wheel   Replace blower wheel
Motor shaft bent   Replace blower motor
Furnace underfired   A) Set gas pressure to “11” W.C. with all appliances running. Replace regulator if not obtainable.
    B) Check burner orifice. It must comply with the furnace’s specifications.
    C) Check duct and return air according to furnace’s specifications.