If your Pentair Mastertemp pool or spa heater has stopped working or is just not functioning as it has in the past, this guide is designed to help you troubleshoot, diagnose, and fix the issue.
Table of Contents
- How does a Pentair Mastertemp work?
- Check water flow
- Error codes on the automation panel
- Reset the swimming pool main power supply
- Errors on the heater control panel.
- Errors on the heater control circuit board
- How to bypass sensors to test functionality
- How to test the thermal regulator
- ERR PS
- ERR HLS
- ERR AFS
- ERR IGN
- ERR AGS
- ERR SFS
- 126 Error
How does a Pentair Mastertemp Swimming Pool Heater work?
A Pentair Mastertemp heater is actually a very simple appliance that becomes more complicated due to all of the interlock protection. It uses a heat exchanger that is warmed similar to a tankless water heater to warm the water. To control the water temperature a manifold is designed to open up to let water exit back to the swimming pool once it is at its desired temperature.
The heater has a blower that pulls air and gas into the burner flame holder. A sealed heat exchanger surrounds the flame holder and discharges gases out of the flue stack or exhaust. Water is drawn through the heat exchanger through the top 2” PVC pipe going into the heater. It then is regulated via a thermal regulator to control how long it remains in the heat exchanger before exiting via the lower 2” PVC pipe back to the swimming pool.
This whole process is controlled by a control circuit board located behind the user-controlled buttons. There are many safety interlocks that will prevent the heater from working if they sense anything other than their pre-programmed conditions. Something as simple as low flow or a dirty sensor is enough to prevent the heater from operating.
Check for proper swimming pool water flow.
Anytime a heater issue is discovered, the first thing to check is the water flow. Clean or backwash your filter system to ensure there is no blockage or slowdown of flow through the filters.
If your swimming pool is equipped with a saltwater generator, remove and clean the salt cell to ensure build-up is not blocking the water. Something as small as a calcified salt cell or a small bit of debris lodged in a pipe can cause enough of a flow issue, to prevent the heater from functioning properly.
If you are unsure how to clean your filters or salt water generator please watch our instructional videos found below:
Clean your filter
Clean a salt water generator
Once you have cleaned the filters and salt cell and you are sure the water is flowing correctly, there are several places you can look to further research the possible issues with your heater.
Heater Error codes on Pentair Intellitouch or Automation Center
One of the easiest places to look for an error is to check your automation. Many new systems will send alarms to your phone or tablet when things go wrong. If you have a Pentair Intellitouch or another automation center, check for alarms and errors on your panel. Errors could show up as ERR for the inlet water temperature or the outlet water temperature. If you have either of these errors you need to replace your water temperature sensor.
Power cycle the main swimming pool breaker to reset the entire swimming pool electrical system.
Occasionally automation systems, pumps, and heaters will start working again if you reset the main pool breaker. Just like a computer needs to be restarted every once in a while to work at its peak performance, a simple power cycle can solve many issues. Leave the breaker off for a minimum of 30 seconds and then cycle it back on.
If resetting the power breaker and checking flow does not solve your heater issue, there are many other places that show errors. Two of the most common locations for error codes and lights are on the main heater control panel and the heater circuit panel.
Errors on the Heater Control Panel
The first place to look for errors is on the heater panel itself. There are several codes that can be present. Also, there are three small lights that can help direct your troubleshooting.
The three lights that may be illuminated on your heater are as follows:
Service Heater-Indicates an issue with your heater system. One or several sensors or switches are causing the heater to not function normally. Continue reading through this guide to troubleshoot.
Service System-This usually indicates a flow issue or pressure switch failure.
Heating-If this light is solid, the heater is heating. If this light is blinking, it means the heater is trying to light but something is preventing ignition. Usually this is a problem with an ignitor, sensor, or thermal regulator. Check your ignitor and sensors to verify where the problem lies.
There are also numerous codes that will show up on the actual display of your heater. They are as follows:
- ERR PS – Error of the pressure switch or flow problems.
- ERR HLS – High limit switch
- ERR AFS – Error of the airflow switch
- ERR IGN – Ignitor Error
- ERR AGS – Automatic gas shutoff error
- ERR SFS – Stack flue sensor
- E05 – Stack flue sensor
- E06 – Stack flue sensor
- E01 – Water temperature sensor error
- 126 – Water temperature sensor
Errors on the Circuit Board
If you do not see any of these codes on the heater control panel itself, it may be necessary to check the led lights on the back of the control circuit board. Older model heaters do not show the ERR codes in the same way the new heaters do on the main control panel. On the back of the control panel there is a circuit panel. It has an area that has a list of lights that will illuminate when there is a problem detected. Each light has a code written next to it in white. Find the light that is illuminated to see what code your heater is presenting.
To gain access to these additional codes you will need to remove remove two of the heater side panels. Each panel has 4 screws. You then remove 4 wing nuts located under the top heater cover in the corners. Flip the heater lid upside down and find what LCD light is illuminated to get the error code.
The following codes may be illuminated:
PS – Pressure Switch. This switch is located above the inlet water PVC pipe.
HLS-High Limit Switch. This switch is located on bottom left corner output side of the manifold
The HLS light could also indicate a broken manifold valve. This is a rare occurance and quite an expensive repair. Contacting a swimming pool service company in your area is suggested before attempting this repair.
Pentair Mastertemp 400 Manifold
The thermistor doesn’t have a code but sometimes indicates E01. It is located on the top left side of the manifold
Afs-air Flow switch connects to vacuum lines. It is located where the clear plastic vacuum lines connect.
Ags-automatic gas shutoff. This sensor is located on the right side of the manifold below the water pressure switch
Sfs-stack flue sensor. This sensor is located on the exhaust stack.
Insert photo of where everything is located
How to test interlock sensors and switches to determine functionality
If you want a quick easy way to determine if a specific sensor or switch is faulty, you can use a jumper cable to bypass the switch from the system. Cut a 3-inch piece of 14 gauge wire and strip both ends. Remove the two wire leads to the sensor you believe is at fault. Connect the two leads together with the wire jumper. Attempt to run the heater with the jumper installed between the two wire leads. If the heater functions properly, replace that sensor or switch and retest the functionality. If the heater functions normally after the replacement of the sensor or switch you have resolved the issue. If not, test further.
How to test a thermal regulator
The thermal regulator is located between the 2-inch inlet water and 2-inch outlet water pipes on the manifold. Use a screwdriver sideways to unscrew the thermal regulator housing to remove the regulator. Take the regulator and place the end under hot water. If the regulator opens and closes under hot water the regulator is functioning properly.
ERR PS – Pressure Switch
ERR PS and PS means there is not enough water flowing through the heater. Check to make sure the filters are clean, the pump is running normally, and there are no blockages in the lines due to a clogged SWG, full skimmer basket, or pump basket issues. The pressure switch may have also just gone bad. Run a jumper between the two wire leads as explained here to bypass and check the function of the pressure switch.
If you determine your pressure switch may be the cause of your swimming pool heater issue you can purchase a replacement switch at the following link:
ERR HLS – High Limit Switch
ERR HLS or HLS means that the water temperature after the 1st pass through the heat exchanger is more than 135 degrees Fahrenheit. This could be due to low flow, a bad HLS sensor, or a bad thermal regulator. Over time these sensors and regulators can corrode and must be replaced. Make sure the wires are connected securely to the HLS sensor and that the temperature regulator operates normally.
If you determine your high-limit switch or thermal regulator may be the cause of your swimming pool heater issue you can purchase a replacement at the following link:
ERR AFS – Air Flow Switch
ERR AFS or AFS indicates a blockage of air or low flow of air. This could be due to a bad blower motor, blocked inlet, or clogged or leaking vacuum line. Bypass the AFS to determine if it’s a sensor problem. Replace the vacuum lines with ¼ I.D. by 3/8 O.D. clear plastic tubing to ensure no obstructions are interfering with vacuum pressure to the sensor. When you select the heater to “ON” ensure you can feel air flowing out through the exhaust and that you hear the blower turn on.
If you determine your air flow sensor switch may be the cause of your swimming pool heater issue you can purchase a replacement switch at the following link:
If you would like to purchase clear plastic tubing to replace your vacuum lines please visit the following link:
ERR IGN – Ignitor
If you have an ERR IGN error or If you do not show any errors on the main heater control display or on the circuit board one possible cause could be the ignitor.
Typically when the ignitor is bad your heater will try to cycle on. You will smell gas and see a blinking heater light. This means the heater is calling for ignition and heat but for some reason the heater is unable to light off. It will usually cycle and try to light off a few times before giving a service heater light code.
To test the ignitor disconnect the electrical plug from the ignitor. Place your multimeter in ohms mode. The leads should test at 50-100 ohms. If it tests at anything less than 50 or more than 100 replace your ignitor. A replacement ignitor can be found at the following link:
ERR AGS – Automatic Gas Shut-off
If the water temperature after the 2nd pass through the heat exchangers is more than 140 degrees Fahrenheit your automatic gas shutoff sensor may be bad. When the AGS sensor fails your front panel buttons will be disabled. After replacing the AGS sensor you may need to reset the heater to restore function to the buttons. To purchase a replacement AGS sensor click the following link:
ERR SFS – Stack Flue Sensor
This error indicates the stack flue/exhaust temperature is more than 480 degrees Fahrenheit. This could be due to a blockage in the stack flue or a bad sensor. Bypass the sensor using a jumper cable on the two leads to see if the sensor is causing the error. Replace the stack flue sensor with the part at the following link to see if the heater function is restored. Similar to the AGS sensor you may need to power cycle the heater to restore functionality to the heater buttons.
Stack flue sensor replacement part
This error indicates an open stack flue sensor.
This error indicates a shorted stack flue sensor
For E05 AND E06 error codes follow the following flow chart to resolve.
This error indicates an open water temperature sensor, To clear the error the HEATER OFF button must be pressed.
This error indicates a shorted water temperature sensor.
For E01 AND 126 error codes follow the following flow chart to resolve. (This flow chart can also help diagnose and resolve AGS, AFS, HLS, and PS errors.)