Problem explanation
When the blower runs but ignition fails, the furnace has likely completed its initial safety check but failed to sense airflow or verify flame. This typical 'no-heat' condition often points to a restricted return, low gas pressure, or a faulty sail switch preventing the gas valve from opening.
Step-by-step diagnosis
1. Verify Thermostat Settings
Ensure the thermostat is set to 'Heat' and the temperature is at least 5 degrees above current room temperature. Check for any 'Low Battery' indicators on the display which can prevent signal transmission.
2. Check Battery Voltage
The furnace blower must reach a specific RPM to trigger the sail switch. If your house batteries are below 12.2V, the motor may spin but not fast enough to allow ignition. Connect to shore power or start the engine to verify.
3. Confirm Propane Supply
Verify tank levels and ensure the service valve is fully open. Light a stove burner to purge air from the lines and confirm steady gas pressure is reaching the appliances.
4. Reset Furnace & Sail Switch Basics
Turn the thermostat off for 30 seconds to clear a 'lockout' state. If the blower runs but you never hear the rapid clicking of the igniter, the sail switch is likely stuck or failing to engage due to low airflow.
5. Inspect Vent & Return Air Path
Check the exterior exhaust port for insect nests or soot. Inside the coach, ensure no rugs or furniture are blocking the return air intake, as restricted airflow prevents the internal safety switches from closing.