Why Pentair Mastertemp 400 Won’t Turn On [5 Easy Solutions]

Pentair Mastertemp 400 won’t turn on for various reasons. Among the possible reasons, reduced flow of water, exchanger plugging, level of pH and alkalinity, membrane pattern, etc. can be the regular ones. You can change the flow and level of the water in your pool to solve this issue or keep the level of pH or alkalinity on a regular check to tackle this issue. 

If implying these methods don’t solve your issues, then go through our article patiently to find the right solution to your trouble. Dealing with these common causes gets easy when you find out your problem precisely. Otherwise, it certainly can get risky and harmful. 

Therefore, this article will help you learn the reasons behind this problem and provide the right solution to tackle it at the same time. 

Why Pentair Mastertemp 400 Won’t Turn On [5 Easy Solutions]

There are a few specific reasons behind this problem. Let’s dive into the reasons for which your Pentair pool heater won’t turn on and find simple solutions for them as well as follows: 

Note: You can also read how to fix Pentair heater error codes problems.

1. Issue With Membrane Pattern

The membrane pattern is an integral part of a heater. When there is any issue with this part, your pool heater won’t turn on. 


If your pool heater has issues with the membrane pattern, then when you press the spa and pool there will be no lights to show. When that is the case with your heater, then you have to disconnect the membrane connector from the board. After that, short both the pins at first that are closest to the yellow button. In case your board doesn’t have any issue, then it will make your heater kick on right away. 

2. Usage Of Saltwater

When you use saltwater on your pools, then it can certainly develop corrosion in your pool heater. Because of the corrosion in the wields, Pentair pool heaters often won’t turn on. 


To deal with the saltwater issue, you can avoid salt water in your pool for instance. If you don’t want to do that, then use heat exchangers that are made of cupro-nickel. It will protect your heater from any corrosion to safeguard the power section. 

3. Pinhole Leaks

Leaks in the pinhole can be another reason behind this issue. There are copper tubes available on the machine’s interior which can develop leaks in the pinhole. And that can also be the reason why a Pentair Mastertemp 400 won’t turn on.


You can get new copper tubes to change the outdated ones sitting on your machine’s interior. It will give your machine a new life and therefore it won’t trouble you with any Pentair pool heater not turning on issues. 

4. Alkalinity And pH Levels

Alkalinity levels play a pivotal role in maintaining the power section of a Pentair pool heater. When you use the same pool heater for several years, then the alkalinity level of that heater can erode the tube walls along with low pH levels. That can cause some damage to the power portion and therefore a Pentair heater may not turn on. 


To maintain and balance the optimum levels of alkalinity and pH, you need to check on the heater regularly. When your Mastertemp requires any update or change, then you will need to make that right away. 

So, these are the common reasons for which a Pentair Mastertemp 400 may not turn on easily or have power-related issues. 

5. Faulty Exchanger Plugging

The exchanger plug is an integral part of the pool heater machinery and it plays a vital role in keeping the heater working. But when there is an issue with exchanger plugging, your Pentair Mastertemp 400 won’t turn on easily. 


To deal with this issue and to turn your pool heater back on, you may require to change the exchanger plugging. With a new exchanger, your pool heater may start in no time. 

How To Turn On The Pentair Pool Heater [3 Easy Methods]

As we have already put out a discussion on the reasons behind the power issues of the Pentair Mastertemp 400, dealing with those problems will definitely help us to turn on the pool heater easily. So, let’s get into the details of the process and how to turn on the Pentair pool heater:

Method 1: 

You can turn on your pool heater by connecting the electrical panel box with a new membrane pattern. After connecting the new one with the panel, you just need to switch it on. 

Method 2: 

You need to ensure that you have pressed the right menu. And the electrical panel is functioning in auto mode. Then, press the menu and go down to heat. After that, press and select the option of pool temperature services to turn it on.

Method 3: 

You can turn your pool heater on by resetting the entire system. And to do so, you need to find the metallic box inside of the machine and turn it off manually. Then wait for a minute and turn it on again. It may take a minute or two to restart with a reset. But after that, the pool heater will turn on. 

This is how you can deal with the problems for which a Pentair Mastertemp 400 won’t turn on. But before trying any one of the above-mentioned solutions randomly, you better should identify the reason precisely at first. 


Is there any fuse in the Pentair Mastertemp 400? 

Yes, there is a fuse available in the Pentair Mastertemp 400. It is located inside the heater’s control panel. You should keep the fuse in check from time to time to see if it is blown or not. 

Why does my Pentair Mastertemp 400 keep turning off? 

Incorrect chemistry of water can damage the gas exchanger of your pool heater. It can then lead the heater to trip. The water level of your pool can also be another reason for your heater to get turned off. 

Why does the Pentair Mastertemp 400 keep tripping?

When the condenser coil of your pool heater gets dirty, then it has to function at a higher capacity to match the heating or cooling level. This is the reason for which the Pentair starts to trip mainly. 

How to reset a Pentair Mastertemp 400? 

To reset a Pentair Mastertemp 400, you need to reset the whole system. And to do so, first turn off the breaker and then wait for a minute to turn it on again. It may take some time to start, but the pool heater will reset for sure. 

Where can I find the fuse on my Pentair Mastertemp 400? 

To find the fuse on your Pentair 400, first locate the electrical panel that is next to the heat pump. After locating the electrical panel, you will see a tiny metallic box out there and that is the fuse. 

Final Verdict  

As you have read through the article, hopefully, you have got your solution to your “Pentair Mastertemp 400 won’t turn on” issue. So, from now on, whenever you find your pool heater is not turning on, simply explore our comprehensive solution guide and fix it by yourself. 

However, don’t forget to let us know in the comment box whenever you begin to struggle with any other issue with your Pentair heater. We will be happy to assist you to solve your trouble. 

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