Mastertemp400 breaker tripping while heater is OFF

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J

James L.

Active member
Feb 20, 2025
31
Baton Rouge, La.
Heater breaker trips while heater is OFF.
A couple weeks ago, Mastertemp400 heater stopped working. Checked it over, replaced membrane pad, heater works. Heater circuit board ok. Heater has been working since then. Today, noticed tripped heater breaker. Flipped it on several times, 30-60 seconds later, breaker trips. This is while heater is OFF, and has not been run for a few days, so it's not hot or anything. This morning is the first time this has happened.
When breaker is reset to on, heater will start and fire up as if normal, which indicates to me (but I could be wrong) that all wires are ok, no fuses blown, circuit board ok, membrane pad ok; then breaker trips.
Breaker test button light is not blinking, so I assume breaker is ok.
Com link status ok-no errors. Remote works normally.
It rained here yesterday, but it rains a lot of days here.
Easytouch 8 system.
Any ideas? Thanks.
 
Latest piece of info:
Now breaker is not tripping. I will check it in a few hours to see if it tripped.
Possibly some rain water got into somewhere in the heater and was causing a short, thus tripping breaker. And now after everything has dried out, possibly water that was tripping breaker dried out too, and no tripping.
That heater is not watertight. Membrane pad cover does not keep water out, and it was wet from rain water this morning, and cabinet is leaky as well.
 
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James L. said:
Possibly some rain water got into somewhere in the heater and was causing a short, thus tripping breaker.
Click to expand...

It's more likely a GFCI trip and not a short circuit trip.

Short circuit trips and GFCI trips are two different failure modes. You need to understand the difference to diagnose the problem and what the fix is.
 

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Just saw the two posts above, after I sent this post in.
Breaker test button trips the breaker as expected.
I do not know the difference between a short circuit trip and a GFCI trip, or how to diagnose which it may be, or how to fix it. I'll do some researching to learn about it, and maybe you guys can chime in. Thanks.
 
A magnetic "Short" is a solid short to ground causing more than 100 amps of current or a solid short between hot to hot or hot to neutral.

A GFCI "Short" is a weak connection of hot to ground or neutral to ground causing a very tiny leak of current in the 5 milliamp range.
 
Molded Case Circuit Breakers have three trip mechanisms.

1) Magnetic. Caused by very high current 100+ amps and this is very fast. (About 5 to 10 times the breaker rated current).

2) Thermal. Based on heat. Overload trip time based on amount of overload.

A 20 amp breaker must trip at a sustained current of 27 amperes (135 percent) at less than one hour, and at 40 amperes (200 percent of wire rating) in less than 120 seconds

3) GFCI. Based on comparing current/amps out to current/amps in and tripping if the difference is more than 4 to 6 milliamps.

 

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James L. said:
Just saw the two posts above, after I sent this post in.
Breaker test button trips the breaker as expected.
I do not know the difference between a short circuit trip and a GFCI trip, or how to diagnose which it may be, or how to fix it. I'll do some researching to learn about it, and maybe you guys can chime in. Thanks.
Click to expand...

Electrical GFCI - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
So if it is a ground fault that that is causing the breaker to trip, how does one find where the fault is occurring? I still think moisture is involved (and I read those suggested links and others too, and among causes of faults is moisture), and it is only the heater breaker that is tripping. I have found no burnt anything, smelled no smoke or ozone smells, no bad wires. When everything dried out, the tripping stopped. So, is there a way to find where the moisture (or any fault) is causing the fault/tripping? Spray the heater with a hose?
 
Nothing is going to be burnt with a ground fault. The current loss is low.

Moisture and corrosion often cause a ground fault, allowing enough electrons to flow to ground to trip the GFCI. You have to find the moisture around when the CB trips.

Show us pictures of the electrical box area in the heater.
 
Have you checked the wiring near the fenwal control unit (should be in a metal box inside of the heater?

Also, if im not mistaken the membrane pad and the connected circuit board are powered by a 120 (or 240) to 24v transformer that sits between the exhaust vent and blower inside of the heater.

I believe the on/off fireman's switch only completes the loop for the 24v side of the wiring to the circuit board.

Fwiw, you might want to inspect the wiring in the circuit breaker too. You should turn power off at the breaker to your entire pool sub-panel before checking that or have a professional look at it. It is possible you could have a wiring issue there as well. Inspect the wires and ground connection, making sure they are not loose in the terminals. Also, look for any sign of damage to the wires.
 

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