Pentair Master Temp 400 (yes another thread)

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J

jtrubash

Member
Feb 13, 2025
18
Austin
Hey all, new here and new to having a pool. We recently purchased a house that has a pool and the heater listed in the title. Age is ~8yrs. I'll describe what is happening but can post a video if needed.

When I initiate the heater everything fires correctly and the unit starts to produce heat (both heat through the flue stack as well as exiting water). While this is happening the unit will flash between service heater, service system and heating lights. Majority of the time is spent with the heating light lit but it does continue to flash to the others. During this time the flue stack temp rises as would be expected up to around 300 after a couple of minutes. It is around this time that the unit cuts off producing heat (though air continues to flow out of the stack and the unit stays on) and service unit light stays on. Back of the board shows "AGS" lit. This sequence of events happens consistently.

So far I have tried jumpering the AGS sensor wires, which produced the same result. I have also replaced the control board which also resulted in the same sequence.

I had a contractor come out today who mentioned the unit looked worse for the wear in terms of some corroded areas and recommended replacing the unit. Before I commit the ~$6K to replacing my heater is there anything else I should try to fix the current unit? I'm at a loss and would appreciate any help.

Thanks
 
Welcome to TFP.

Show us pictures of your pool equipment pad and how worse for the wear the heater looks.
 
You have both a tablet chlorinator and SWG.

When was the tablet chlorinator last used? The acids in the tablets can damage a heater. That type of chlorinator should not be used following a heater.
 
jtrubash said:
I did but that implies it is setting off the AGS sensor which I ruled out by jumping the wires
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Show me the sensor and what you did.

If you have not checked the thermal regulator and bypass valve, you should.
 

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Stealing pictures does not show me what YOU did.

That thermal regulator is corroded and needs to be replaced.

Was the thermal regulator tested by seeing if it opens at 120F in a pot of water?

Read the Wiki fully as it explains that your problem is a water flow problem with the internal water temperature getting too high. It is not a sensor problem. There are a bunch of reasons the Wiki describes for why the heater water is not flowing properly. You can go through a structured diagnostic process to try and fix it or you can buy a new heater. Your choice.
 
As @ajw22 above mentioned the thermal regulator and bypass valve. Thermal regulator isn't invasive but the bypass valve necessitates removing the manifold which at that point you'll very quickly see the health of the heater by seeing the condition of the copper tubing of the heat exchanger. If your planning on the manifold removal have a full replacement gasket set for a "leakless" reinstall.
 
ajw22 said:
Stealing pictures does not show me what YOU did.

That thermal regulator is corroded and needs to be replaced.

Was the thermal regulator tested by seeing if it opens at 120F in a pot of water?

Read the Wiki fully as it explains that your problem is a water flow problem with the internal water temperature getting too high. It is not a sensor problem. There are a bunch of reasons the Wiki describes for why the heater water is not flowing properly. You can go through a structured diagnostic process to try and fix it or you can buy a new heater. Your choice.
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I’m clear on why those areas could be the issue but my understanding is that the AGS sensor is the one that would actually detect the water temperature getting too hot and subsequently cutting off the gas supply as a protection mechanism. My thought was that if that sensor is out of the equation and I’m still getting the AGS error that something different is happening. Apologies if my thought process is incorrect.

I can get an accurate picture of what I did when I get home from work
 
jtrubash said:
I’m clear on why those areas could be the issue but my understanding is that the AGS sensor is the one that would actually detect the water temperature getting too hot and subsequently cutting off the gas supply as a protection mechanism. My thought was that if that sensor is out of the equation and I’m still getting the AGS error that something different is happening. Apologies if my thought process is incorrect.

I can get an accurate picture of what I did when I get home from work
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The cycling is indicative of the water temperature getting too high, a safety shutting down the heater, the heater cooling, and the cycle restarting.

Recognize it is a high water temperature problem. That is what you need to find and fix. The heater safeties are doing their job shutting down the heater until it cools and resets.
 
ajw22 said:
The cycling is indicative of the water temperature getting too high, a safety shutting down the heater, the heater cooling, and the cycle restarting.

Recognize it is a high water temperature problem. That is what you need to find and fix. The heater safeties are doing their job shutting down the heater until it cools and resets.
Click to expand...
Does it matter that the heater does not initiate a new cycle on its own? I need to manual restart (cycle power) for it to heat again
 
Did you buy a genuine Pentair Control board?

We have heard of many problems with third party control boards.

Show me a picture of your new control board.
 
That is not a genuine Pentair control board which may be part of your problem.
 

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