Pentair Mastertemp 250 Troubleshooting Guide [11 Easy Solutions]

The common Pentair Mastertemp 250 problems that users often face are the heater not igniting or not turning on and the heater not heating at all.

Plus, the heater going out frequently, air flow issues, cycling on/off, display not working, heating light blinking, and heater turning on by itself are also the troubles from which the users frequently struggle.

pentair mastertemp 250 troubleshooting guide

However, in today’s Pentair Mastertemp 250 troubleshooting guide, we will explore the reasons behind all these issues and give you easy solutions to each problem. So, let’s go on reading…

Pentair Mastertemp 250 Troubleshooting Guide [11 Easy Solutions]

Here are all the issues’ reasons explained with possible simple solutions:

1. Pentair Mastertemp 250 Not Igniting

Pentair Mastertemp not igniting issue has bothered many users over the years. If you’re also one of them, then you need to know the reasons behind Pentair Mastertemp not igniting. Your Pentair Mastertemp 250 won’t ignite because of:

  • Lower gas supply
  • Blocked filter
  • Defective gas valves, gas supply valves, or plumber valves 
  • Faulty transformer 
  • Broken igniter
  • Incorrect thermostat temperature setting 
  • Bad Ventilation
  • Damaged pilot light tubing


  • You can adjust the gas supply according to the manual to resolve this problem. 
  • Clear out all the clogs and dust to unblock the filter.
  • Replace all kinds of defective valves.
  • Purchase a new transformer and install it. 
  • Replace the bad igniter with a new one. 
  • Check out the thermostat setting from the manual and set it according to that. 
  • Due to damaged pilot light tubing, the pilot light can’t stay lit. Replace the defective tubing.
  • Clean all the vents of the heater using compressed air.

2. Pentair Mastertemp 250 Not Heating

Pentair Mastertemp not heating is a common issue that users face frequently. There are different reasons behind this as well. Your Pentair Mastertemp 250 is not heating due to:

  • Faulty or damaged temperature sensor
  • Wrong thermostat temperature setting
  • Blocked filter
  • Malfunctioning ignition system or heating element
  • The trouble with the internal bypass system


  • You have to repair or replace the damaged or faulty temperature sensor based on its conditions. 
  • Change the thermostat settings according to the manual. 
  • Take out the things that are blocking the filter. 
  • Look for the specific portion where the malfunction occurs and resolve it by replacing or repairing the parts. 
  • To fix internal bypass system trouble, consult a professional. 

3. Mastertemp 250 Won’t Turn On

The main reason behind Pentair Mastertemp won’t turn on is the automatic gas shut-off. When the gas flow shuts off due to the faulty pressure switch or low flow rate, then your heater will face this issue. 

Other reasons why the heater is not turning on include:

  • Faulty igniter
  • The defective ignition control module
  • Bad control fuse
  • Malfunctioning of the flue sensor 
  • Defective  membrane switch
  • Tripped safety switches
  • The control panel is not getting sufficient power
  • Blocked filter
  • Corroded heat exchanger


  • If you want to fix this issue, then you need to check out the water flow rate and make sure it is adjusted properly. The water flow rate should be at least 35 GPM (gallons per minute).
  • Ensure that the water filter is properly cleaned. Check and replace the corroded heat exchanger. Set the correct temperature on the thermostat.
  • Measure the voltage of the safety switches, including the high limit switch, Air Flow Switch (AFS) and pressure switch. Replace the defective safety switch.
  • Replace the damaged & defective transformer.
  • Make sure that your heater’s control panel is getting power. For this, check if the thermal breaker is overloaded or the circuit breaker gets tripped. Change the control board’s faulty sub-panel.
  • Besides, check and replace the stuck membrane pad, the corroded or faulty sensor.
  • Also, ensure a proper fuel supply pressure and the thermal regulator is seated correctly in place. Test the continuity of the terminal board’s fuse. Look for blown or faulty control fuse.
  • Change the faulty igniter and the bad ignition module. Finally, check the burner flame holder is securely grounded.

4. Mastertemp 250 Keeps Shutting Off

If your Pentair Mastertemp 250 heater keeps shutting off, it is sure the heater is not set at the correct temperature.

Also, faulty wiring causes insufficient voltage supply, which shuts off the heater frequently. Note down other responsive factors for this issue:

  • Insufficient gas supply
  • Damaged high limit switch
  • Shorted air flow switch or AFS
  • The defective ignition control module
  • Clogged pool heater
  • Faulty temperature sensor
  • Faulty control board.


  • To solve this problem, first, set the accurate temperature on the control. You have to make sure that the set temperature is higher than the pool water.
  • Inspect the wiring connection of the heater. Repair or replace the faulty wiring
  • Ensure the proper gas pressure of the heater.
  • Then access the high limit switch and check it. You can test the switch by jumping it. Replace it if the heater continues running without this switch.
  • Jump the AFS as well and fix the switch issue.
  • Replace the defective ignition control module.
  • Check the pool filter if it is clogged by debris. Clean the filter to ensure proper water flow.
  • Check and replace the faulty temperature sensor and bad control board. 

5. Pentair Mastertemp 250 Air Flow Fault

Pentair Mastertemp 250 air flow fault occurs due to the excessive exhaust temperature detected by the flue stack sensor. It will open the stack flue sensor, and therefore your Pentair Mastertemp heater may shut off entirely. 


Turn off your heater and see if the thermal regulator has been damaged or bad. If it has gone bad or damaged, then try repairing or replacing it based on the condition. This will solve the airflow fault of the Pentair heater. 

6. Pentair Mastertemp 250 Cycles On And Off

If your Pentair heater is cycling on and off, be sure the bad thermal regulator is the leading culprit. Also, when the pressure sensor is damaged by the improper flow of gas from the system, Pentair Mastertemp 250 heater cycles on and off can happen. 

Some other major reasons that lead to this issue include:

  • The damaged ignition control module
  • Bad high limit switch
  •  Incorrect or loose wiring
  • Closed valve
  • Fluctuations in power supply
  • Imbalanced pool water chemical levels
  • Failed control board
  • Deterioration of the heat exchanger
  • Malfunctioning internal bypass

Here are the needed steps that you have to follow to fix this issue with your heater.


  • First up, check the thermal regulator. You will find it in between the inlet and outlet connections of the manifold. Replace if the regulator is defective.
  • To stop the Pentair heater from cycling on and off, you need to change the bad control module.
  •  Access the high limit switch and replace the defective switch. Inspect and change defective internal bypass as well.
  • Ensure that all of the connections of the heater are secured.
  • If the problem is occurring due to a defective control board, you will need a new control board.
  • Check the condition of the valve and ensure all the valves are opened. Also, the water filter should be blockage free.
  • Check out the pressure sensor and heat exchanger. Replace all the defective ones.

7. Pentair Mastertemp 250 Heating Light Blinking

Pentair Mastertemp 250 heating light blinking when the heater is calling for heat but fails to ignite. The leading reasons for such ignition failure on the pool heater include:

  • Faulty flame sensor
  • Broken igniter
  • Defective control board
  • Damaged air flow switch
  • The failed ignition control module

Follow the below guide to stop the heating light from flashing.


  • First up, inspect the flame sensor to see rust build up there. Also, look for any signs of damage or cracks in the sensor. Clean up the flame sensor and replace it if needed.
  • In the case of a bad igniter, locate it near the top of the combustion chamber and replace it.
  • Besides, check and replace the ignition control module or ICM.
  • As the defective control board causes ignition failure, you need to change it.
  • Now check if the AFS switch has tripped. Ensure the blower is working properly and reset the tripped AFS switch. In case the blower is working fine, there has surely been a defective AFS. Replace it.

8. Pentair Mastertemp 250 Turns On By Itself

When the Pentair heater turns on by itself, it refers to the fact of automation issue. This mostly happens when the heater senses the temperature is lower and there is a call for heat. Then the heater automatically turns on. 

Also, a faulty thermistor, glitches in the power supply, a bad touchpad, and a malfunctioning control board cause your heater to turn on by itself.


  • You can easily fix this problem by adjusting the automation settings of the heater. For this, you need the owner’s manual to learn how you can do that. Or, you can call in a technician to do that.
  • If the issue persists from a bad thermistor, you need to replace it.
  • Also, check the touchpad if it is faulty. Change the defective touchpad.
  • Access the control board and check it. Replace the board if it has gone bad. 

9. Pentair Mastertemp 250 Display Not Working

Your Pentair Mastertemp display not working is a major issue because you won’t be able to put any command on it when the display isn’t working.

The problem mainly occurs due to a lack of power supply. A blown fuse or a defective control board is also highly responsible. 


  • To resolve the power supply issue, you need to measure the transformer’s input line voltage in a voltage meter. It should give a reading of 120V or 240V. 
  • If you are not getting the correct voltage, be sure the transformer is faulty. Replace it. Otherwise, check the ignition control module.
  • Check the fuse, whether it is broken or blown, and replace it. 
  • Finally, you need to replace your control board as it might be the reason for causing the heater display not working.

10. Pentair Mastertemp 250 Ignition Lockout

Pool heater ignition lockout is one of the most common that pool heater owners may face. Every digital pool heater, including Pentair mastertemp 250 equips an automatic ignition system. It allows to turn on and off the heater in order to maintain the desired temperature at all times. 

If the heater temperature exceeds during ignition, the high limit switch shuts down the unit and prevents overheating. Here the heater will go to the ignition lockout. 

When the ignition lockout occurs, your Pentair Mastertemp 250 not igniting issue will appear. Here the lockout function needs to be reset to get the heater back into operation. 

Below we have included the instructions to troubleshoot the system and diagnose the problem.


  • First up, you need to reset the circuit breaker. Turn the breaker “Off” and “On.” 
  • Then, put the system in “Standby” mode by pressing the “Mode” button on the digital heater control panel.
  • Now, press the Up & Down buttons. Hold the button simultaneously until the indicator light and digital display flash rapidly. 
  • When the heater goes into the adjustment mode, it may show an ignition error code on the digital display. Fix the errors.
  • If the display doesn’t show an error, press the Up & Down buttons to set the desired maximum temperature.
  • Press the “Mode” button to set the temperature.
  •  If the indicator light flashes slowly, that means the heater is out of ignition lockout mode. 

11. Pentair Mastertemp 250 Leaking Water

If your Pentair heater is leaking water,  it could be due to the following:

  • Chemical or sanitizer damage
  • Damaged heat exchanger
  • Loose connection to the pressure switch
  • Defective internal bypass
  • Broken gasket
  • Crack in pool heater
  • Condensation leakage


  • To resolve the chemical damage, you need to drain the heater and clean it properly. You can use an acid solution to clean the pool heater and to prevent the heater from any damage caused by chemicals.
  • Repair or replace the damaged heat exchanger and broken gasket.
  • Now check if the internal bypass valve is broken. If yes, replace it.
  • If still, the water is leaking, check if there are any cracks in the pool heater. Contact a certified plumber. 


Why Won’t My Pentair Mastertemp 250 Fire?

Your Pentair Mastertemp 250 won’t fire due to the dirty filter of your swimming pool. This is the most common cause behind Pentair Mastertemp not firing. A dirty pool filter will restrict the flow of the water forcibly and the heater won’t be able to fire. So, clean the pool filter to fix it.

How can you reset your Pentair pool heater?

To reset your Pentair heater, you need to turn the power down to the heater for 10 seconds at least. Then, you need to reset the heater from settings. After that, you need to turn on your heater and it will reset all the functions to default. 

How do I fix the power issue of my Pentair heater?

In order to fix the power issue of your Pentair heater, you need to check the connection out first and ensure that the heater is getting enough power. If it still doesn’t fix the issue, then you need to open up the heater to find any damaged parts inside it and repair or replace it. 

Why is your Pentair heater blowing cold air?

When the heater’s filter is clogged then it can lead to the heater blowing cold air. Replacing the filter with a new one doesn’t solve this issue. Because the dust and debris reach the unit and stay there even if you change the filter. So, you need to clean the unit first and then the filter to get warm air. 

Final Verdict

Hopefully, this article was able to help you sort your problem out and show you the right solution for it as well. In that case, it would be better if you strictly follow our guidelines and use our methods to fix your trouble. Because only then you will be able to sort your Pentair Mastertemp 250 Troubleshooting. 

But if this article and the methods in it don’t show you the path to find the problem and solution, then let us know in the comment section about your issue in detail. We would be happy to help you to solve your problem in no time.

About William

William is the founder of He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

4 thoughts on “Pentair Mastertemp 250 Troubleshooting Guide [11 Easy Solutions]”

  1. Hi,
    Our MasterTemp 250 heats our spa to 97 degrees, and not anymore than that. We can only set the temp to 97 on “spa”. We can set the temp to 99 on “pool”. But, either way, the water does not feel as hot as either 97 or 99.


    • Hi Jeff

      Generally, this type of issue happens due to one or more reasons like an inadequate gas supply to the heater, a Faulty temperature sensor, a defective thermostat, a malfunctioning heating element, or a blocked filter.
      Plus, a faulty high-limit switch can also be responsible in some cases which may signal the natural gas pool heater to turn off before you get the desired hot water.

      Well, to fix the issue, inspect all the above-mentioned issues one by one & try to find out the main culprit behind the pool heater temperature issue & fix it.

      Alternatively, you can contact the Pentair customer support center for help.

      Wish you all the best!

  2. Issue I’m having I did not see addressed, basically when you turn the power on to heater, display panel works fine and heater tries to fire, after two attempts it goes to Service Mode than the display panel just locks up, wont let you turn on/off. If you reboot power supply, it comes back but then the sequence just repeats itself. I replaced the display panel but that didn’t work. Any thoughts?

  3. My Mastertemp 250 keeps blowing the internal 1.5 amp fuse. Usually when I power it up nothing happens until I turn it on, but now when I put in a new fuse, I turn the power on and all of the lights and displays light up, then the fuse blows.
    My local repairman said he didn’t know what to do. Any suggestions?


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