Pentair MasterTemp 400 keeps shutting on and off- then stops trying

[davedive]

Hi All,

I've opened my pool and tried heating the water some. The heater kept shutting on and off, and the service LED would come on. I would hear an awful clattering in the pipes, like loose parts swirling around. My pool guy came out and replaced an internal part (manifold?) and it worked again with no clattering. But 2 weeks later the heater is misbehaving again, comes on fine but after like 7 minutes the heating stops and the heater amber light starts blinking. After 35 seconds it fires up again and runs for about 20 seconds then pauses again, and on and on, 20 secs on / 35 secs off/ 20 secs on, etc. Any thoughts? Thanks!

 

[ajw22]

We need to know what part has already been replaced.

Check the thermal regulator and the internal bypass valve.

Check all valves are in the proper position.

What is your filter pressure PSI? What type of filter do you have? When was it last cleaned?

Short cycling of a heater is often caused by low internal or external water flow. A dirty filter can cause it.

Show us pictures of your system.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[davedive]

Thank you for the help! I will try to answer some of these questions, and attach pictures.
I'm waiting to hear back from pool guy to find out what he replaced but he mentioned it was a part where pieces of plastic had broken off causing the clattering noise.
How do I check the thermal regulator? Do I need to disassemble the pipe coming out? I think I replaced this 2-3 years ago. How do I check the internal bypass valve? I've never replaced it.
All valves are in proper position (see pic)
Filter pressure is about 12 with the filter pump on 3 (usual level). When I have the filter pump on 4 it jumps to 20. I have a pentair filter and just cleaned all 4 cartridges yesterday.
See attached pictures
Thanks!

 

[ajw22]

 

[ajw22]

How do I check the thermal regulator? Do I need to disassemble the pipe coming out? I think I replaced this 2-3 years ago. How do I check the internal bypass valve? I've never replaced it.

It is all in the Wiki...

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[ajw22]

This is the internal bypass.

To fully see and access the internal bypass the manifold must be removed.

You can see the spring in the heater inlet.

You can see the disc in the thermal regulator hole.

It works like a spring check valve.

The disc gets pushed open by water pressure to allow some water to bypass the heat exchanger but the disc can break off and allow too much water to bypass the heat exchanger.

Usually, you can just look in the hole for the thermal regulator to make sure that the disc is still there.

It can break off and go out of the heater outlet.

The red arrow points to the disc.

If the disc is missing, the hole will look like the bottom picture.

 

[ajw22]

Filter pressure is about 12 with the filter pump on 3 (usual level). When I have the filter pump on 4 it jumps to 20. I have a pentair filter and just cleaned all 4 cartridges yesterday.

Remove all four cartridges, run the heater, and see if you still have the problem.

 

[davedive]

OK thanks. Have not heard back from my pool guy but I'm 99% sure he replaced that internal bypass. There was a clattering noise before he worked on it and no noise after. I will check the thermal regulator and try removing the cartridges and running it that way. Thanks again!

 

[ajw22]

As a test you can try running the heater without the thermal regulator.

 

[ajw22]

OK thanks. Have not heard back from my pool guy but I'm 99% sure he replaced that internal bypass. There was a clattering noise before he worked on it and no noise after. I will check the thermal regulator and try removing the cartridges and running it that way. Thanks again!

How much did he charge you for that repair?

 

[davedive]

How much did he charge you for that repair?

Just got the bill. Thermistor, Manifold bypass valve kit, thermal regulator kit, labor and tax= $630. Looks like he replaced everything which is good.

 

[davedive]

Since everything has been replaced not sure what else to try here. Tried to heat the pool again this AM and found it goes fine for about 15 to 20 minutes, then starts the cycling thing- it's weird. If I try to heat the spa it does the same thing but not as bad. I can get the temp up but it takes longer than normal.

 

[JamesW]

Remove the thermal regulator and show looking into the hole.

Show looking into the inlet.

Run without the thermal regulator as a test.

Test thermal regulator.

Check the stack flue temperature.

Check Flame Current.

 

[JamesW]

Filter pressure is about 12 with the filter pump on 3 (usual level). When I have the filter pump on 4 it jumps to 20.

What speed is level 3 and level 4?

 

[JamesW]

Since everything has been replaced not sure what else to try here.

Don't assume that it was done or done correctly or that the parts have not already failed.

Look for error LEDs.

 

[JamesW]

the service LED would come on.

Service System or Service Heater?