Pentair Mastertemp 400 Pool Heater

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AndyFla

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Nov 6, 2018
22
Melbourne Fl
Issues with keeping boiler lit. The heater would fire up and go for about 10 mins then I get a HLS (High Limit Switch) error. After a few min (about 2-3) it fires back up. It takes a long time to get to temp (101). I replaced the HLS sensor and it fired up again first try. The initial Temp was 74 (I live in Florida) and when it reached ~80 it again got the HLS error. After 2-3 min, it fired back up and would do this off and on till it gets to temp. I have replaced the HLS, Air Flow Switch, and Thermal Regulator all within the last two weeks. I am at a lost to what this is. Could this be normal operation and i just never noticed it? Thanks for your help in advance.

Andy
 
Pentair Master Temp 400 Pool and Spa Heater HLS Error Light Repair Replace Manifold Bypass Valve - YouTube

Mastertemp bypass valve

If you remove the thermal regulator, you should be able to reach up and feel the round disc.

Or, you can open the top union and look inside to see if the bypass is intact.

The internal bypass is a spring loaded check valve that opens based on the water pressure in the inlet portion of the manifold.

At high pressure/flow, the disc is pushed open to allow water to go directly from the inlet to the outlet without going through the heat exchanger.

This prevents too much water from going through the heat exchanger.

Sometimes, the little disc will break loose and then too much water bypasses the heat exchanger.

With insufficient flow, the water in the heater will over heat and give a high limit error.

Do you have an external bypass valve?

If yes, you need to make sure that it's not fully open. Depending on the pump size, you might need to close the external bypass anywhere from about 50% to 100%.
 
I took apart the manifold and cleaned it out. I saw no damage to any parts to include the bypass valve. I put it back together and fired it back up. It still has the same problems. About every two or three degrees in temp rise it gives me the same HLS error than clears itself after a minute or two. It gets to temp but does seem to take a little longer to do so than before.

Any more help would be appreciated.
 
Turn the heater on and then press and hold the Pool button until the display shows the exhaust temperature to see what that shows.

Do you have a picture of the system?

Do you have a regular 400 model or a 400hd model?
 
Ok, I have (I think) the Mastertemp 250 NA. On the inside cover it does not stipulate if its HD or not so I am assuming its standard. I have attached pics for you. I fired up the system and pressed the spa on button to see the exhaust temp. It climbed to 280, then the system shut down (really just gave me an error but the fan was still running). Then a few (~2 min) minutes later it fired back up again and reached 280 degrees again and shut down. Continues this till it reaches max temp.
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It's acting like a low flow issue. That can be a bad thermal regulator, a bad internal bypass, a scaled heat exchanger, low flow from the system or some combination of the issues.

Make sure that the filter is clean.

What pump do you have?

What are the chemistry readings?

Are you getting any scale in the pool?

Try running without the thermal regulator in place to see if that makes any difference. Just a test, don't leave it like that.
 
I cleaned the filter and basket before all the troubleshooting. The pump is a Intelliflo VS-3050 Variable speed programmable pump. The pressure out of the jets is strong. The chemistry is perfect (I have it checked weekly). I have a Salt Chlorine system so it really is perfect. No scale or anything. When I took apart the manifold it look very clean (some small pieces/specs of stuff) and the bypass valve looked great. Not broken. Will it fire if the thermal regulator is removed? I will try.
 

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The thermal regulator blocks flow through the heat exchanger until the water heats up to reduce the amount of condensation forming on the heat exchanger coils from cold water running through the coils.

Even when the thermal regulator opens up, it's still a small opening. Removing the thermal regulator just allows water to go through the heat exchanger continuously.

The hole is bigger with the thermal regulator removed, so you get better flow.

The only other thing that I can think of is if the heat exchanger is scaled.

If nothing else works, I think that I would try descaling the heat exchanger.

I would remove the thermal regulator to allow flow through the exchanger and then rig up a small circulation system to circulate a descaler mix through the exchanger.

What rpm are you running for the pump speed?

What is the filter pressure at that speed?

Ask the Pool Guy: 10 Steps to Descaling A Pentair Pool Heater - YouTube

For the descaler mix, I would look for a product designed for descaling that's safe for copper. Acid will work, but it can be aggressive to copper.

Other than that, I'm not sure what else to check.
 
OK, you are on to something here. I removed the thermal regulator and it started up fine and continued to run till it got to ~90 degrees (I was afraid to continue without the regulator). The exhaust temp only reached ~165 and remained steady. I have attached pics of the regulator. I just replaced the regulator a week ago, could I have gotten a defective one? Or could it not have been seated correctly? Getting close here. Thanks a bunch.

IMG_3685.jpg
 
Maybe try a different regulator.

The regulator is to prevent condensation from forming on the heat exchanger due to cold water continuously circulating through the heat exchanger.

The regulator opens at a preset temperature when the heater fires.

If the thermal regulator is not opening correctly, the flow through the heat exchanger will be insufficient and the water will overheat and trip the high limit.
 
No, the chemistry was good, maybe a little acid now and then, and the chlorine was high due to some cold snaps we have had, but thats it. Stabilizer and hard solids are all in line. That pic was the new regulator, maybe been installed three weeks tops.
 
Ok. Maybe compare it with the next new one for reference.

Hopefully, the new, new regulator will work properly.

You can test the regulator by putting it in hot water to see if it opens. It should open at about 130 degrees Fahrenheit.

Are you using fasdpd to test chlorine?

Some test kits bleach out at high chlorine levels and people keep adding chlorine without realizing that the chlorine is actually too high.
 
I have a salt system and get it tested at pinch-a-penny weekly. I don't add chlorine at all. The salt system is normally set at 13-17% during the winter months and ~25 during the summer. My pool is an acid eater so I only have to add stabilizer once every 6-8 months and a cup or two of acid every week. Thats it. Oh Salt when that gets too low, maybe once a year. When I say chlorine is high, its 5-10 when it calls for 3-5. I took out the regulator and it works fine, no issues and it fires up and stays lit till it reaches 101 degrees. I will order another regulator and see if that fixes it. This regulator looks nothing like the one I took out in terms of corrosion. It is discolored based on the new one, but no where near the one I took out.
 

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