Stuck on this issue after a lot of troubleshooting and repair attempts.
Behavior: Burner lights fine. Clean blue flames. Readout water temp on panel rapidly rises (beyond 100F at unrealistic rates for normal flow) until heater kicks off due to lack of heat demand. After heater kicks off and pool pump is still pushing water, temperature continues to rise, often all the way to 150F before stabilizing and eventually coming back down.
Checked water flow into pool, very good pressure. No air, all water when bleeding from filter.
Replaced thermistor (twice). Same temp behavior.
Vacuumed, soft-brushed, and low-pressure water-cleaned heat exchange fins. Same temp behavior.
Removed and tested unitherm governor. It lengthened in hot water like you would expect. (Governor O-Ring was a bit worn, added lube and have a replacement coming tomorrow.)
No scaling or other buildup present anywhere in the unit that I can see.
I'm stumped. It doesn't seem like a control board issue, because the temperature readings are normal (~70F) until heating starts. I would be surprised if there is scaling inside the heat exchanger, I have the version with cupronickel, and my pool chemistry is normal.
Behavior: Burner lights fine. Clean blue flames. Readout water temp on panel rapidly rises (beyond 100F at unrealistic rates for normal flow) until heater kicks off due to lack of heat demand. After heater kicks off and pool pump is still pushing water, temperature continues to rise, often all the way to 150F before stabilizing and eventually coming back down.
Checked water flow into pool, very good pressure. No air, all water when bleeding from filter.
Replaced thermistor (twice). Same temp behavior.
Vacuumed, soft-brushed, and low-pressure water-cleaned heat exchange fins. Same temp behavior.
Removed and tested unitherm governor. It lengthened in hot water like you would expect. (Governor O-Ring was a bit worn, added lube and have a replacement coming tomorrow.)
No scaling or other buildup present anywhere in the unit that I can see.
I'm stumped. It doesn't seem like a control board issue, because the temperature readings are normal (~70F) until heating starts. I would be surprised if there is scaling inside the heat exchanger, I have the version with cupronickel, and my pool chemistry is normal.
