Pentair MasterTemp 400 Keeps Shutting Off [9 Easy Fixes]

The common reasons why your Pentair MasterTemp 400 keeps shutting off are incorrectly set temperature control, incorrect wiring, low gas pressure, and a wet or damaged high-limit switch.

Besides shorted or defective AGS, faulty ignition control module, clogged pool filter, faulty temperature sensor, and bad control board are also responsible for your MasterTemp not staying lit.

Keep reading our Pentair MasterTemp 400 troubleshooting guide to solve this issue. 

Table Of Contents

Pentair MasterTemp 400 Keeps Shutting Off [9 Easy Fixes]

Here, we will take an in-depth look at the reasons for Pentair MasterTemp 400 shutting off. Our simple solutions should fix your heater ASAP. 

1. Incorrectly Set Temperature Control

Your pool heater will shut off once the set temperature is reached. In case you have set the temperature control at a temperature lower than the pool water, your Pentair MasterTemp 400 will shut off immediately.

Note: You can also read how to fix Pentair MasterTemp 400 common problems.


Set a higher temperature on the control. Setting a temperature lower than 68° F is bad for your heater and continually operating at that temperature risks condensation. For adults, temperatures up to 100° F are okay. 

To reset the temperature, first, press POOL/SPA. The current setpoint and water temperature are displayed on the display.

To increase or decrease the temperature of the water setpoint, press Up/Down. The heater will start heating if the current water temperature is below the Setpoint water temperature.

2. Incorrect Wiring

This is a common reason for your pool heater to trip. Faulty wiring can result in an insufficient voltage supply, which causes the heater to trip frequently. A defective capacitor or a loose wire could also be to blame.  


You need to inspect the wiring of your Pentair MasterTemp 400. Double-check all the wiring connections and replace any damaged wires.

Ensure that all the connections are tight. The Pentair MasterTemp 400 wiring diagram given below should guide you.

Pentair MasterTemp 400 wiring diagram

3. Low Gas Pressure

Low gas pressure can be why your Pentair MasterTemp 400 keeps shutting off. Your heater can’t operate without appropriate gas pressure. 


You can test the gas pressure by doing the following.

Step 1: The first thing to do is remove the back panel. Use a ⅜ inch nut driver to take out the four screws. Lift up and remove the panel. Towards the right, you should be able to place the gas valve. 

Step 2: With a 3/16-inch Allen wrench remove the little plug on the side of the gas valve. Shut off the gas valve and connect a manometer to it. You will need to put in an adapter first. 

Step 3: Attach the hose and turn on the gas valve. Now check the pressure reading. A reading of 10 inches of the water column is ideal for your Pentair heater.

Step 4: Turn your heater on. If your gas pressure drops more than about one to two inches of the water column when it fires, you don’t have enough gas pressure. 

Contact your local gas company for assistance.

4. Wet Or Damaged High Limit Switch

When water gets in the high limit switch, it creates a short to ground and limits the amount of current or voltage getting to the gas valve.

On the other hand, a damaged high-limit switch can read heater temperature incorrectly which can be why your Pentair MasterTemp 400 starts and stops.


You need to access the high-limit switch by taking off the side cover of your unit. It has three screws holding it together.

To test whether the high-limit switch is the culprit, jump the switch and run your heater without it.

If your heater continues running without shutting down, it means your high-limit switch has been compromised.

In case it is wet, try air drying it and starting the heater again. Replace the high-limit switch if necessary.

5. Shorted Or Defective AGS

AGS stands for automatic gas shut-off. If the heat exchanger outlet temperature exceeds 140° F, the valve opens and shuts off the gas supply.

A defective or shorted AGS means that your heater may shut off at unpredictable times.


To be sure that the AGS is causing your heater to shut off, you need to jump the AGS and see if your Pentair MasterTemp400 keeps turning off still. 

Locate the AGS by removing the side panel and testing it. Like the high limit switch, your AGS can also get wet causing it to short. Let it dry if that is the case. You may need to replace the AGS.

6. Defective Ignition Control Module

Your ignition control module may be failing to get a flame signal. This can stop your heater from starting up properly and cause it to shut down each time you try.


You need to replace the ignition control module. 

Remove the left side panel of the heater. The heating jacket’s four bolts must be removed. Disconnect the Max-E-Therm heater. 

Separate the wires and connectors that link the legacy ICM. Remove the two mounting screws from the older ICM. Remove the original ICM unit from the heater.

Insert the ICM into the Junction Box chamber of the heater. When replacing the ignition control module, connect the wires according to the manufacturer’s instructions.

Remove and reassemble the heating control panel assembly. Make sure the control panel can be adjusted without having to bend over the exhaust vent.

7. Clogged Pool Filter

A clogged pool filter stops regular water flow and overheats the heater pump. This triggers the high-limit switch to shut off the heater.  


You can easily clean your own pool filter. You must disassemble the filter cover in order to remove the elements.

There are a total of four of them. Using a hose, thoroughly wash them out. Reassemble the filter once it has been cleaned.

8. Faulty Temperature Sensor

A faulty temperature sensor can read the temperature of the water incorrectly. If the heater thinks that the water is hotter than it actually is, your Pentair MasterTemp 400 will shut off earlier than it should.


Replace the temperature sensor. 

9. Bad Control Board

A bad control board can also be why your Pentair MasterTemp 400 keeps shutting off. 


Test the control board with a multimeter to be sure that it is at fault. Pentair customer service can help you acquire a new control board and replace the old one. You should contact them for Pentair MasterTemp 400 control board replacement. 


Is there a fuse in a Pentair pool heater?

Yes. You will find a fuse in your Pentair. Pentair Sta-Rite Max-E-Therm pool and spa heaters, as well as Pentair MasterTemp pool and spa heaters, are compatible with the Fireman’s switch fuse. 

How do I reset my pool heater?

You just need to shut off your pool heater and after waiting 10-15 minutes, turn it back on.

Where should a pool temperature sensor be installed?

Install the sensor in the open, in a shady spot, and away from air conditioners. Take a look at this temperature sensor installation guide for further instructions. 

Does a pool heater cause water loss?

Yes, during winter you will. This happens to owe to the temperature difference to the environment. If you suspect a pool leak, turn off any automatic filling devices you may have.

Is it normal for a pool heater to drip water?

Yes. Condensation draining from the heater causes water to drip from the heater after running for 10–30 minutes. This is completely normal and anticipated. To be sure, switch off the heater while keeping the rest of the equipment running. Everything should dry out again.


Hopefully, you now know what to do when Pentair MasterTemp 400 keeps shutting off. In case you are facing any issues with your Pentair heater, leave us a comment. We will get back to you soon with our best advice.

About David

David is a man who loves doing research and finding out the best solution to any type of heating appliance issues like heaters and fireplaces. Whenever he finds the perfect solutions to any issues of heating appliances after doing in-depth research, he loves to share them with his readers. In fact, his aim is to help his readers to fix the issues with their heating appliances easily.More about us .

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