Pentair MasterTemp 400

The heater unit is not turning on
Check the breaker
Check the automation and alternatively press the POOL ON on the heater unit to make sure the heater is asked to turn on.
If the breaker is on and you are sure the heater should be running, you’d need to check the voltage at the control module. If the control module is getting power, and the fuse is not blown, it’s safe to assume the control module is not working and should be replaced.
The heater unit is turning on, but I don’t hear the blower
The first thing to check is if the blower motor is getting power, if the blower motor is getting power it’s most likely the control module is not working and should be replaced.
The heater unit is turning on, but it’s not heating
Before you move on, verify the following
The blower motor is turning on
After a short duration, you smell gas
If you do not hear the blower motor turn on check “The heater unit is turning on, but I don’t hear the blower”
If you do not smell gas, check that your gas supply valve is opened. If the valve is opened and you don’t smell gas after 10 sec. Of turning on the heater unit, you should check the heater's gas valve.
If you’ve verified that the blower motor is turning on and that you smell gas, but the burner is not coming on, then follow this procedure.
Check the heaters sensors
Check the igniter
Check the control module
Replace what is not working according to specs.
Checking the heaters sensors
You’ll need to remove the front, back, right side, and lid from the heater unit.
Behind the controls, you’ll find the control board and on that, you should see 5 led’s. They are marked PS, HLS, AFS, AGS, and SFS.
If one of the led is on, replace the sensor accordingly.
PS is your pressure switch, located on top of the manifold.
HLS is your high-limit switch, located on the bottom left of the manifold
AFS is your air flow sensor, located next to the blower motor and connected to two tubes
AGS is your automatic gas shut-off switch, located on the bottom right of the manifold
SFS is your start flue sensor, located on the exhaust
The HLS and the AGS are what we refer to as on/off switches, and sometimes they are faulty even though the led hasn’t come on.
To check this, and to make sure you do not have a problem with the two sensors, you can short them using a simple wire connected between each of the connectors to the switch. You can short both sensors, then turn on the heater and check if it will fire.
The one sensor that is not represented on the back of the control panel is the terminator, this sensor is telling the control module and you the temperature of the water. This means this sensor is a variable sensor and can be partially faulty or fully faulty. If the thermistor is fully faulty you will see the error code EO1 on your control panel. If it’s partially faulty you will see a higher or lower-than-usual temperature reading.
Check the igniter
You’ll find the igniter on top of the burner kettle. Unplug the connector (White connector with two grey wires) and check the resistance on the igniter side connector. You should be seeing somewhere between 40 and 75 ohms on a working igniter. If you’re not, then the igniter is faulty and should be replaced.
Check the control module
You’re blower is running, you are smelling gas, no faults light up, the control panel is not reporting any errors, the sensors are working and your igniter is working.
In this case, you should remove the control module, remove the back plate on the control module and check the soldering on the print. It is a common problem on the control module that soldering fails. In 4 out of 5 cases, you’d be able to solder the missing connections on the control board, but keep in mind a control module is no more than $150-200.