RV Furnace Trouble Shooting

Before attempting to trouble shoot your furnace be sure you understand the sequence of operation. Also see definitions.

This list is a guide only, of the more common causes of furnace failure, it is by no means complete.

Electronic Ignition Models (DSI)

Before going through the list below, these items should be checked.
Gas Pressure should be 11" of water column.

Power supply, DSI furnaces require 10.5 VDC to 13.5 VDC to operate.

Ducting, check for the correct number of unrestricted ducts and outlets.

Check the return air path, be sure it meets the required minimum sq. in.

RV furnaces are not approved for use with filters.

• Blower doesn't run
  Possible causes:
  • no power
  • thermostat
    Warning: Never cross the thermostat wires with the thermostat connected. You will destroy the thermostat.
    • dirty contacts
    • bad on/off switch
    • broken or shorted wires
    • bad thermostat
  • bad time delay relay or thermostat relay
    You have time delay relay if there is normally a delay from the time you turn the thermostat up to the time the fan actually comes on, usually around 30 seconds.
    Instant on blower = thermostat relay
  • loose or broken wire or poor ground
  • tripped circuit breaker or blown fuse - not all furnaces have either of these
  • bad motor
• Blower runs - no ignition
  Possible Causes:
  • low voltage
  • bad fan motor
  • bad gas supply or low pressure
  • exhaust or intake vents obstructed
  • bad or dirty sail switch
  • bad limit switch
  • bad or out of adjustment electode
  • bad electrode wire
  • bad gas valve
  • dirty burner
  • bad control board
  • NOTE: the design of electronic ignition furnaces is such that once the thermostat closes and calls for heat the blower will run until the thermostat is satisfied, the battery runs to low to run the motor, the motor wears itself out or the thermostat is shutoff.
• Burner ignites - goes out after a few seconds
  Possible causes:
  • low gas pressure
  • intake or exhaust vents obstructed
  • dirty burner
  • electrode(s) out of adjustment, dirty, or defective
  • bad control board
• Sooting - usually shows as a black streak above the exhaust vent.
  Possible causes:
  • dirty burner - common with older models that use a cast iron burner
  • low gas pressure
  • intake or exhaust vent obstructed
  • bad fan motor
• insufficient heat
  Possible causes:
  • low gas pressure
  • poor gas supply - crimped gas line, under size tanks in below freezing temps.

Sequence of operation

This is generic and applies to most DSI model furnaces.

• Thermostat calls for heat.
• Thermostat relay or time delay relay is energized and allows power to the blower.
• Blower motor runs up to speed.
• Sail switch closes at 75% of rated blower speed.
• Power goes through the limit switch to the ignition control board.
• The control board begins trial for ignition, opening gas valve and initiating ignition spark.
• Burner ignites.
• Thermostat reaches setting and opens.
• Burner shuts down.
• Fan runs briefly to cool furnace.