Pentair mastertemp 400 HD

[mobgod]

Hello all I'm having a issue with the service heater light, can't get my heater to fire, did a reset the light comes on for heater than goes back to service heater. Code I'm seeing on boot is R12

Thanks in advance

 

[JamesW]

Check under the board for an error light.

 

[mobgod]

Check under the board for an error light.

I have AGS

 

[mobgod]

AGS seems to be auto gas shut off, but why?

 

[JamesW]

The automatic gas shut-off (AGS) switch opens if the heat exchanger outlet temperature goes above 140° F
(60° C).

If the heater isn't firing, the AGS sensor is probably bad. I would replace that first.

You can check the AGS sensor with a multimeter. Set to ohms and check sensor for continuity with the heater unpowered and the wires off of the sensor. The sensor should be closed (0 to 1 ohm).

If that doesn't work, the control board is the likely problem.

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