I just replaced the old hayward H400idl2 heater with a used Sta-Rite SR400NA Heater. After checking the new plumbing for leaks and purging all the air I fired the heater and everything was running normally. After running for about 3 hours I had wife check on heater and she claimed that the temp display was showing 112 while it was running. The temperature was set at 90 deg F and initial water temp was 82.
So this sounds strange, the heater should have shut down and not been running if the temp was 112.
She checked the heater again after a few hours and the heater was off and the display said 90. I had her bump the temp up to 92 and the heater fired and ran normally. When I returned from work the heater was off and the service heater light was on. Display showed 91 deg.
I checked the led's under the keypad and there were no diagnostic lights lit. Followed trouble shooting procedure and no lights illuminated after a 5 second power off and then on with the set temp at 93 deg. The heater fired normally.
What I notice after playing with it for nearly an hour as long as the set temp is 3 or 4 degrees higher than the current water temp the heater fires and runs normally.
If the set temp is 1 degree higher it seems like heater will turn on and off then there is a fault when it does not light for whatever reason.
After searching the forum and the internet I see that it seems like there are a lot of problems with the temp sensor (and incorrect temperature readings on the display). I wonder if the output is erratic and it's causing some issues with the controller as it closes in on the setpoint?
When the heater fails to ignite I did see that there were 3 flashes coming from the control module indicating ignition lockout. Again there were no diagnostic led lit on the control board below the control panel.
I have 1 1/2" commercial grade gas meter with 1 1/2" gas line approximately 20ft feeding the pool heater. There is less than 18" of 3/4 gas pipe between the 1 1/2" pool heater feed line and the heater. There should be plenty of gas volume available to the heater under all circumstances. The rest of the house has a 1 1/2 main feed line with branches feeding the rest of the gas appliances. The tankless water heater is fed from the 1 1/2" main feed line at the end of the line. I have never had any issues with any of the other appliances with our without the pool heater, BBQ, dryer and tankless running at the same time.
If anyone has any ideas Id appreciate the feedback.