Heater turning on and off after 90 degrees

[Brianlitt]

I have a pentair master temp 400 and once I get in the 90s my heater seems to run for a minute or two, stop heater and throw a service heater light, and then feels like it’s actually pushing cold water for a bit. A couple minutes later the process repeats.

Any idea what I can check? No error codes are displayed.

 

[ajw22]

Check the thermal regulator.

If not the thermal regulator check the bypass valve in the header.

If you are replacing the bypass valve then also replace the thermal regulator.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[Brianlitt]

Will do that, thanks!

 

[Brianlitt]

I took off the thermocoupler and it responds as expected based on the video.

However, when I go put it back in I walk by the pool and a bunch of white powder surrounded both drains. The pool was obviously off while I was doing the thermocoupler check.

Any thoughts?

I went ahead and swept the white powdery and turned on my pump after replacing the thermocoupler.

 

[ajw22]

I doubt the white powder has anything to do with your heater problem.

What drains are you talking about? Post some pics.

 

[Brianlitt]

I doubt the white powder has anything to do with your heater problem.

What drains are you talking about? Post some pics.

It was the main drains at the deep end. I didn’t take a pick as I randomly panicked. It’s as if the drains were volcanoes of white powder. Maybe 12” in each direction.

 

[ajw22]

Please create your signature with details of your pool and equipment so we know what we are discussing.

The main drain takes water in. Water does not flow out of it to blow powder out unless you have some unusual plumbing setup.

 

[mknauss]

When the heater drained due to pulling the temperature regulator, I suspect there was some back flow to the pool.

But white powder is odd. Have you added any solid chemicals lately? Did the powder readily dissolve?

 

[Brianlitt]

When the heater drained due to pulling the temperature regulator, I suspect there was some back flow to the pool.

But white powder is odd. Have you added any solid chemicals lately? Did the powder readily dissolve?

It did readily dissolve. I’m confused - was hoping it was a clue to the heater.

I know it sounds stupid, but based on the amount I almost feel like it was trapped pool conditioner. When I added pool conditioner in the past it didn’t change my CYA levels and I was so confused. Too light to be DE and there’s no other white chemical I have added in ages.

Is my next step to try to get the issue to occur again, take off the front panel of the heater and look at the error lights?

 

[mknauss]

Odd on the powder. Not scale if it dissolved easily.

Heater diagnostics is not my strong suit. @ajw22 can guide you better on that.

 

[ajw22]

Is my next step to try to get the issue to occur again, take off the front panel of the heater and look at the error lights?

I doubt the error LEDs will tell you anything if the heater short cycles, resets, and restarts.

Have you stood by the heater and observed the way it sounds and what the temperature display on the heater panel shows as it cycles?

 

[Brianlitt]

I doubt the error LEDs will tell you anything if the heater short cycles, resets, and restarts.

Have you stood by the heater and observed the way it sounds and what the temperature display on the heater panel shows as it cycles?

So I feel like the heater thinks the temperature is hitting before it actually is when I stand next to it.

I was watching the apps temperature vs the temp on the mastertemp and they do not agree. Also, I believe the app more based purely on feel. I hate 102 water and that’s what the heater read while the app said 97-98

 

[mknauss]

What automation do you have? Please add that to your signature.

 

[Brianlitt]

I have IntelliCenter. Updating my signature as we go along. I updated my signature but it doesn’t seem to show when I post. Am I missing something

 

[mknauss]

If you are on a mobile device, turn it sideways to see signatures. I see it with the update via my laptop.

If the Intellicenter and heater are connected correctly, the Intellicenter is controlling the heater.

 

[ajw22]

So I feel like the heater thinks the temperature is hitting before it actually is when I stand next to it.

I was watching the apps temperature vs the temp on the mastertemp and they do not agree. Also, I believe the app more based purely on feel. I hate 102 water and that’s what the heater read while the app said 97-98

The app uses a separate water temperature sensor and does not matter for the purpose of diagnosing a heater problem.

The heater temperature will shut down the heater before the IntelliCenter reaches the set temperature.

I still think it is the thermal regulator and/or the bypass valve. It could also be the thermistor in the heater reading high. I am confident your problem is one of those three things.

You can check the thermistor using a multimeter and a 10K resistor.

The temperature sensor is a 10K thermistor. You can measure its resistance with a multimeter.

Temperature Sensors - Further Reading

www.troublefreepool.com

For a test replace the thermistor with a 10K resistor.

If the temperature stays at 76F while the IntelliCenter heats the water to 102 then you have a problem with the thermistor.

If the heater still will not heat to 102 then you need to check the thermal regulator or the bypass valve in the header.

 

[Poolbreh]

The pool appears to be fairly new. How old is the heater? The powder substance most likely was DE. TFP recommends the sock method for CYA, CYA will stain the surface if it sits on it. I would increase the speed of the pump temporarily while running heater and see if this fixes issue.

 

[ajw22]

What is your filter pressure?

When did you last backwash the filter?

How old is the pool and equipment?

What speed are you running the pump?

 

[Killer95Stang]

I've had the same issues as you with my Mastertemp 400 twice in the last 7 years. Both times it was the thermal regulator. Both times it looked fine, but I replaced it anyway and it worked. Not scientific at all, but that worked each time. While you have the thermal regulator out, make sure the manifold bypass is not broken. I purchased one, but each time I had the thermal regulator out, it was fine.

The white powder you see coming from the drains is DE powder backflowing from your filter. For some odd reason, my pool is plumbed similar to yours. Whenever I open anything in the system for a long enough time, I get powder out of filter going back into the pool from the main floor drains. Either vacuum it up or have your robot take care of it.

Personally, I'm out of warranty, so spending $50 on a regulator is a no-brainer, because the service call is a few hundred dollars and most likely will add a marked up thermal regulator.

 

[Brianlitt]

Interesting - I guess it’s worth a shot. My build is actually new so I’ll first reach out to my pool builder. I don’t mind fixing small stuff on my own but free is free.


I actually backwashed and did a full filter clean about six weeks ago. The DE does make the most sense as what was discharged. I run the pump at 2800 which gets 40 gpa on my pool. My filter pressure is just slightly above where the backwash pressure was, it looks good.