1. Dirty heat exchanger
2. Incorrect “Stack limit setpoint”
3. Faulty sensor
1. Inspect and if required clean the combustion chamber and/or heat exchanger.
2. Unless installed in Canada with PVC exhaust venting, set “Stack limit setpoint” to maximum setting of 220ºF (104ºC). In Canada PVC exhaust venting is limited to 149ºF (65ºC).
3. Check resistance of sensor and compare to thermistor resistance chart,
