Mastertemp 400 Cycling...driving me crazy!!

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Mine is in its 4th season and I had to replace the thermal regulator. Heater was short cycling but not giving any codes. Have you tested the thermal regulator? I placed it in 130, 140, 150 degree water and it did not open. I finally placed it in 190 degree water (water temp was dialed in with my Stagg electric kettle) and it opened, albeit it was popping like it was bound up. A new thermal regulator did the trick.

Good luck.

--Jeff
 
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The thermal regulator should open at 120 degrees Fahrenheit as shown on the part.

The high limit switch should open at 135 degrees Fahrenheit.

So, you have a 15 degree window between the two.

If the thermal regulator opens too late or the high limit opens too early, then you can get a HLS error.

The stack flue temperature is good so I would guess that the high limit switch is opening too early.

If the thermal regulator was bad, the stack flue temperature would probably be too high.



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Running without the thermal regulator might prevent the problem because you get more flow without the thermal regulator, which reduces the outlet temperature and it might be below the high limit switch opening point even if it is opening too early.

So, it's important to verify exactly where the HLS is opening.

I would plan to replace the HLS in any case.
 
I talked with Pentiar today. They had me jumper the HLS to see if the error returned. It did not, and the heater ran without interruption, so they are sending a HLS as well as a thermal regulator just to be safe. I plan to replace them one at a time so I know what fixed the issue.
 
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It might be a combination of both.

If the thermal regulator opens a little bit late (130 vs. 120) and the HLS opens a little too early (125 vs 135), then you can get the problem.

The window is only 15 degrees, so if both are off by 10 degrees, then you have overlap and an error.
 
I dare say, touch wood, that this is now behind me. I replaced the HLS and the thermal regulator, and the cycling seems to have stopped. Since Pentair was unable to get a single service company to respond to my warranty request, I talked them into sending me a new Fenwal flame control unit for my hassle. Since the membrane and PCB had been replaced in the troubleshooting, that upgrades me to RS485 control. I installed the Fenwal, ran a new control wire, jumpered the fireman's switch, deleted the old heater, added a new connected one and BAM - easy as that. At this point, I'll at least have a history of error codes that is more specific if I continue to have issues. Thanks for all the help - as always!

Wes
 
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Well. So much for that. This is like peeling an onion. Fix one fault and the next appears. I guess I get to make another call to them tomorrow. I think I got a lemon...
 

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