Pentair MasterTemp 400 Blower Not Working [6 Easy Fixes]

Your Pentair MasterTemp 400 blower not working can be caused by a number of issues.

Dirt and debris, incorrect wiring, line voltage between pins 1 and 3, no power to the blower during ignition, bad Ignition Control Module, and defective control board are the possible causes.  

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

Table Of Contents

Pentair MasterTemp 400 Blower Not Working [6 Easy Fixes]

You may have the Pentair MasterTemp 400 service heater light on when the blower isn’t working. The AFS light being on signals one of the most common Pentair MasterTemp error codes.

It means that the airflow switch is open and the blower has failed to establish adequate airflow. We will take a look at what can cause your blower to stop working as well as the simplest solutions to these causes. 

1. Dirt And Debris

It could be that your blower motor is in peak condition but it is caught up in dirt and debris. 


Ensure there is nothing blocking your blower from turning. Sometimes cleaning up the blower and removing the cover to the blower motor and using a screwdriver to manually turn it can make the blower start running.

2. Incorrect Wiring

An incorrectly wired blower will not turn on. It could be that one of the wires has come loose or has been damaged in some way. 


On the Ignition Control Module and Control Board, double-check the wiring between the 24 VAC and IND terminals.

At the terminal strip, double-check that wires BM and F1 are properly connected. Check the Pentair MasterTemp 400 wiring diagram given below for reference.

Pentair MasterTemp 400 wiring diagram

3. Line Voltage Between Pin 1 And 3

You need to disconnect the blower and start up your heater. During ignition try, to check on line voltage between pin 1 and pin 3 of the heater’s blower connector.

If you find a line voltage, that means the blower is defective. Otherwise, move on to point 3.


Unfortunately, there is no other solution than to replace the blower.

4. No Power To Blower During Ignition

If your blower isn’t getting power during ignition, the blower motor needs to be replaced. On the other hand, if power is there, you probably have a defective control board or Ignition Control Module.


Here’s how to test power.

  • When the heater initiates ignition, the cables leading to the blower should show 240 volts from the red to the black wire. You can test the power at these black and red wires by disconnecting the blower plug.
  • Get your multimeter to test the voltage on the wires.
  • When the heater is trying to turn on, the red wire should get the power supply immediately. So, before the heater tries to start, the reading on your multimeter should be 120 volts on that leg.
  • The black wire does not receive power until the blower is turned on. Power is applied to black when the heater tries to start, and the voltage reading should be 240 from red to black.

If you get the correct readings, then your blower is fine. The issue is something else. But in case, you don’t get the required readings, replace the blower.

5. Bad Ignition Control Module

The ignition Control Module is essential to time the startup of your Pentair MasterTemp 400 heater. A bad Ignition Control Module can prevent your blower from turning on.


You need to replace the Ignition Control Module. The following instructions will guide you through the entire process of replacing the Ignition Control Module, ICM of your Pentair MasterTemp 400. 

Step 1: Remove the heater’s left side panel. The four bolts on the heating jackets must be removed. Remove the Max-E-Therm Heater from the equation.

Step 2: Disconnect the legacy ICM’s connecting connectors and wires. Remove the legacy ICM’s two mounting screws. Remove the heater’s original ICM unit.

Step 3: Place the ICM inside the heater. compartment for the Junction Box The two mounting screws hold the item in place.

Step 4: Connect the wires according to the manufacturer’s instructions for replacing the ignition control module.

Step 5: Remove the heating control panel assembly and reassemble it. Make sure you can adjust the control panel without having to lean over the exhaust vent.

6. Defective Control Board

The control board controls almost all the functions of your pool heater. A bad control board can cause many problems with your Pentair MasterTemp 400 including the blower not running. 


You need to replace the Pentair MasterTemp 400 control board. Contact Pentair MasterTemp 400 customer service to get them to send you a new control board.

Watch this video on Pentair MasterTemp 400 control board replacement for elaborate instructions.


How do you unlock the Pentair pool pump?

For 3 seconds, press and hold the “1” and “Quick Clean” buttons. The screen will show the “Enter Loc Code”. Enter your four-digit keypad lockout code. “Loc oFF” will appear on the screen and will scroll over it. The lock on the keypad has been removed.

What does a thermal regulator do in a pool heater?

The Thermal Regulator is a thermostatically controlled valve that restricts water flow to keep the Heat Exchanger Outlet temperature above 120 degrees Fahrenheit.

Why does my Pentair pool pump keep shutting off?

Overheating. Many pool pumps are intended to switch off automatically if they begin to overheat for safety concerns. Thermal overload switches are the mechanisms that execute this function. If your pump keeps shutting off, it’s possible that the thermal overload switches have failed.

Is it OK to run the pool pump 24 hours a day?

Your pool size, the efficiency of the heater pump and filter, and the state of your pool are just a few factors that affect the answer. However, most pool cleaning experts recommend not using a pool pump for more than 8 hours every day.

How often do I backwash my pool?

Backwashing your pool once a week or in conjunction with your planned maintenance is a good rule of thumb. Backwash your filter until the pressure indicator on the filter reads 8-10 PSI  over the starting level or “clean” pressure.


Hopefully, you now know how to troubleshoot your Pentair MasterTemp 400 blower not working. Enjoy the warm swims!

Read our article on Pentair MasterTemp 400 common problems troubleshooting guide to become a pool heater repair pro. 

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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