Pentair Mastertemp 300 Heater Won't Turn Off

[JamesW]

Should I still replace the membrane?

Probably.

So, should I pull the fireman's switch in the heater, or the timer, or disconnect the power to the heater as the videos you showed me, or just let it stay as is for now with the gas valve turned off and let it run like it is now (no blower or heater running) until I try changing the membrane tomorrow?

I would disconnect the Fireman's Switch at the heater.

 

[DeBo22]

Probably.

I would disconnect the Fireman's Switch at the heater.

Got it. So pull the two wires you put an arrow to in the pics above, right?

 

[ajw22]

Your heater is not running with the blower and gas off.

It is fine the way it is.

 

[JamesW]

It might still try to start and cycle through the Call-for-Heat Sequence with the blower and ignitor coming on.

The Fireman's Switch is easy to disconnect and it is safer to have it disconnected.

The Fenwal is probably going into Lockout due to no Flame Sensed.

However, the Lockout can expire or be reset when power is cycled causing the heater to attempt to go through a call for heat startup sequence.

Lockout Recovery.

Recovery from lockout requires a manual reset by either resetting the thermostat, or removing 24 VAC for a period of 5
seconds.

On models with automatic reset, if the thermostat is still calling for heat after one hour, then the control will automatically reset and attempt to ignite the burner.

 

[DeBo22]

Thank you all...I pulled the firemans switch just in case.