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. Refer to 14.0 Annual Maintenance and Inspection and Supplementary Documentation section 2.0 System Piping.
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 stack sensor and compare to thermistor resistance chart.
