Pentair Mastertemp 400

HouTex

LifeTime Supporter
Mar 7, 2011
413
Houston, Texas
My Mastertemp 400 is about 3.5 years old and I had my first issue with it two days ago.

Starting temperature was 76 degrees (can't believe the water is still so cool in late May in Houston) and the target temp was set to 95. For the first 30-40 minutes the burner cycled on and off every 3-4 seconds and the temp slowly rose to the low 80's. The heater light flashed when it turned off meaning that it's waiting for the burner to ignite. The service light never came on. I've never had an issue with water flow or gas flow. I cleaned my cartridge filters over the weekend, but I don't believe that would cause a problem with water flow--it should improve it.

After about 40 minutes the unit finally stayed on and it reached the target temp after about 1 hour and twenty minutes. We had heavy rain throughout the day and I wonder if that had something to do with it. I haven't tried it again to see if it was the rain.

I've found a couple of threads with similar issues. Any ideas?
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,049
FL
Cycling on/off like that can be a number of things. You ruled out water flow so the others are, over heating due to bad flow control, thermo regulator, or bad temp limit. But I would say that if it keeps working, maybe it fixed itself.
 

HouTex

LifeTime Supporter
Mar 7, 2011
413
Houston, Texas
UPDATE: Well now the unit comes on for a few seconds (the gas lights and the blower blows), but then the gas and blower shut down and the service heater light comes on.

I smell gas as it lights, but it's not extremely strong. Is this normal? It also makes a high pitched squeal that it didn't used to make. When I have time I will take off the cover and see if any error lights are lit on the control panel. But does anyone have any ideas in the meantime?

I've never had a problem with gas flow or water flow.
 

HouTex

LifeTime Supporter
Mar 7, 2011
413
Houston, Texas
I took the top off of the unit and there are no error codes. The unit would start and run for a while (about 30 minutes the first time) but it eventually would shut off. I turned the unit off and on and the burner would start and it would run for a while and eventually stop. It's clearly not working the way it should.

The big problem is corrosion. The combustion chamber is very rusty. I don't see any water leaking from the chamber but it's very rusty on top, down the sides, and at the exhaust tube. Other than the chamber it looks fine inside and there are no error codes. How rusty can the combustion chamber be before it should be replaced? I checked online and found replacements for about $700 total for the top and bottom of the unit. I wonder if it's worth trying to repair?
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,049
FL
I would check the thermo regulator to see if it's all gunked up.
 
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