Heater wont stay on keeps cycling

kohlzor

Member
Apr 25, 2020
19
Shrewsbury, MA
Hi, I have a Max-E-Therm 400 pool heater, which keeps cycling on and off. I noticed that when it starts heating it will go up to 250 on the display and then shut off, it then cools down to 180 before starting again which is a few seconds later. This is continuous as long as the heater is on.
I have replaced the thermal regulator but that doesn't seem to be the problem. Any suggestions? The service light does not come on.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,049
FL
250?? How old is the heater? Shut everything off and check the thermistor and see if it is all corroded as that can be an issue was well. Also check the Hi-Limit switch while you are at it. Although if the Hi-Limit was an issue you should be getting an error and LED light for it.

And as usual, make sure you have good water flow.
 
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kohlzor

Member
Apr 25, 2020
19
Shrewsbury, MA
The heater is 4 years old. I will try to check the thermistor tomorrow hopefully its easy to access.
Yea 240-250 is when it turns off, like I can see the temp on the display strat ticking up hits 240-250 and burner goes off temp starts ticking down to 180 and kickbacks in. Rinse and repeat consistently.
 

kohlzor

Member
Apr 25, 2020
19
Shrewsbury, MA
So the thermistor seems to be fine as the temperature of the water is being detected correctly. The 250 that was being displayed was the exhaust temperature.
Still not sure why it’s cycling the exhaust temperature goes to 250 and shuts off and starts cycling.
so far I have replaced the thermal regulator and thermostat. Not sure what else could be causing the continuous cycling, most things point to thermal regulator but I checked and the new one opens and closes as it should and it goes straight in the heater so don’t think that is the problem.
 

kohlzor

Member
Apr 25, 2020
19
Shrewsbury, MA

Pool Clown

In The Industry
Sep 5, 2008
2,136
Silicon Valley, CA
The physical or mechanical bypass could be cracked or broken and not regulating properly, causing the water inside it to over heat. However, they usually do some knocking or banging just before the heater cycles off. Not always particularly loud, but you can hear it.
 

kohlzor

Member
Apr 25, 2020
19
Shrewsbury, MA
Gonna check the bypass next and replace the hi limit as well.
Is it normal to smell gas when the heater is firing? Since it keeps cycling I do smell gas and only when it starts it stops during the cycle off period.

The physical or mechanical bypass could be cracked or broken and not regulating properly, causing the water inside it to over heat. However, they usually do some knocking or banging just before the heater cycles off. Not always particularly loud, but you can hear it.
 

kohlzor

Member
Apr 25, 2020
19
Shrewsbury, MA
Hey folks quick update had some techs out today and they thought it was the thermal regulator, but i had replaced it and they checked and it seemed fine.
the bizarre thing is we can get the heater to run with the covers off but when we put both covers back on the cycling starts. If we leave half of the cover on it works but with both continuous cycling. They checked the wires and everything looks good they seem pretty stumped at this point anyone ever encounter anything like this?