Safety first: Turn off power before accessing the supply plenum or control board.

1. Locate the supply air sensor: On some Dettson models, a thermistor or temperature probe is installed in the supply air plenum or on the discharge side of the furnace.
2. Inspect wiring and connector: Ensure the sensor harness is plugged firmly into the control board and that the wires are not damaged.
3. Check sensor placement: The sensor should be fully inserted into the airstream, not hanging loose or touching metal surfaces that could skew readings.
4. Test sensor resistance: With power off, disconnect the sensor and measure resistance with a multimeter. Compare to Dettson specifications for room temperature. An open or shorted reading indicates a bad sensor.
5. Replace sensor if defective: Install the correct Dettson replacement sensor, route wiring away from hot surfaces, and secure it properly.
6. Reset and test: Restore power and run a heating cycle to confirm E11 is cleared.

Dettson furnace displays E11; blower may run at low speed continuously without heating.

Possible Causes