Hi all,
Pool season is about to be over here in western PA and my pool heater has started giving me some trouble.
For reference, I have a Pentair MasterTemp 250. Installed in 2012. We bought the house in 2021 and the heater worked fine last 2 years.
When I turn the heater on, it goes through its regular on sequence, the gas is ignited (I hear the whoosh sound), and hot air starts coming out of the exhaust. But within 5s, I hear a relay click and the heating turns off (no more hot air from the exhaust). The heater tries this sequence again after 15ish seconds, and the same results. It runs for 5s and then turns off. After 3 attempts the service heater LED is on and it stops any further heating attempts.
I have looked behind the front panel, and I don't see any error code LEDs on. I have also checked the following sensors:
1. Water pressure switch: Working, I see a short on the multimeter, when the flow rate is sufficient. For now, I am running my VSP on max speed while I debug this issue, so I don't think the flow rate is an issue.
2. HLS: Working, I see a short on the multimeter.
3. AGS: Working, I see a short on the multimeter
4. Thermistor: Measured the resistance and it seems to match the water temperature
5. Air flow switch: Working, checked with a multimeter
6. SFS: Again, I can see the SF temperature go up when the heater is running for 5s, it goes up to 125. But since the heater turns off, after 5s, it stops rising.
7. Thermal regulator: I saw on some threads that this can be caused by the thermal regulator not moving. I checked the regulator. Initially, I suspected it and replaced it (it was a little corroded), but the issue persists even after regulator replacement.
At this point, I am not sure what else I can do. It appears that the heater tries to fire (indeed starts heating), but some sensor tells it that there's a fault and it turns itself off. Where this could be, I am not sure.
Any suggestions and guidance for the next steps to troubleshoot will be really appreciated. Thanks so much!