How To Fix Rheem Pool Heater High Limit 2 Fault [Solved]

The “Rheem pool heater high limit 2 fault” defines that the high limit sensor is open due to the raising temperature of the system. 

This typically means the temperature inside the inlet/outlet header has exceeded the 135F temperature. For this, the HL switch opens and shuts off the heater.

rheem pool heater high limit 2 fault

The major reason for tripping the switch is the build-up of scale internally in the heat exchanger and producing excessive heat.

Plus, low water flow, corroded unitherm governor, and a faulty thermostat or automatic internal bypass valve lead to the Rheem pool heater HL2 error code. 

At times, a defective high-limit switch is the root culprit or rarely a faulty control panel causes the error. 

Thoroughly read out this effective guide to get the best solutions for high-limit 2 faults on the Rheem pool heater.

Rheem Pool Heater High Limit 2 Fault [7+ Easy Solutions]

Here we have tracked down the 7 major reasons responsible for the high-limit sensor error with all well-proven solution processes. 

rheem pool heater

Let’s glance at the table below to learn all the probable reasons with quick solutions:

Probable Reasons

Possible Solutions
Corroded heat exchangerCheck for corrosion in the heat exchanger.
Low water flowClean the blocked air filter & dirty impeller. Clean the clogged strainer basket. Check for low water levels. Ensure the pressure switch has perfect continuity. 
Corroded thermal governor & internal automatic bypass valveReplace the corroded UG and bypass valve.
Malfunctioning of the thermostatReplace the faulty thermostat
Defective high-limit sensorReplace the bad high-limit sensor and add thermal paste
The Control panel is giving faulty readings due to an internal circuit board issueReplace the defective control panel.

1. Calcified Heat Exchanger

High limit 2 fault mainly occurs due to increasing temperature in the system. Forming scale in the heat exchanger is the root culprit in case of reducing water flow and overheating the heater.

calcified heat exchanger

The heat exchanger is one type of metal alloy tube of the heater which uses hot water from a boiler (or solar-heated water circuit) to warm up the pool water.

Corrosion is the major factor of heat exchanger failure in process applications. High chemical concentrations from the feeders and chlorinators cause rapid corrosion in the heat exchanger.

Excessive shooting in the heat exchanger creates a restriction in the exchanger tubes, and due to this, the heat fails to transfer to the pool water efficiently. 

Then, a lot of heat passes through the flue, which trips the switch.  So, at this first troubleshooting stage, you will need to inspect and check the heat exchanger for a buildup of soot.

How To Clean Pool Heater Heat Exchanger

Follow the below step-by-step guide to clean the calcium deposit and scaling from heat exchanger tubes:

how to clean pool heater heat exchanger

Step 1: Initial De-assembly

First up, disconnect the heater from the power connection. Also, shut off the water supply by closing the valves. Leave the heater for some while to let it cool. 

Now, remove the screws from the pool heater top panel and the side access covers and take those off. Then, detach the front door panel.

Step 2: Inspect The Heat Exchanger

Remove the screws holding down the flue collector. Also, remove the heater screws, securing the heat exchanger in place. Then, lift the heat exchanger straight up and place it on a clean surface.

Step 3: Clean The Heat Exchanger

To clean the scale, apply a degreaser to the heat exchanger tubes using a soft-tipped brush. Leave the degreaser for some while to loosen the soot. Once done, wash the heat exchanger using a garden hose. 

Now check the exchanger tube for any type of physical damage or leakage. If yes, you may want to have it replaced.

Precautions: Avoid using a wire brush to clean the heat exchanger as it may create sparks that ignite gases trapped in the soot.

2. Low Water Flow

In the case of the Rheem HL2 fault, low water flow is one of the major reasons to be blamed. The heater requires adequate water flow to fire and operate correctly. 

The recommended water flow rate for most pool heaters is a minimum of 20 GPM (75 L) and a 70 GPM (265 L) at maximum.

When the flow rate is lower than recommended rate, it is a clear indication that there has some malfunction in the entire system which needs your attention. The significant factors behind low water flow include:

  • Blocked water filters or impellers, restricting the water flow.
  • The pressure switch has stopped operating due to an incorrect voltage.
  • Incorrect installation of the bypass valves.
  • Faulty plumbing fitting.
  • Low water level.
  • Blocked baskets by debris and dirt.

Now get knowledge of how you will fix the water flow issue on your pool eater to diminish the high limit 2 faulty.


i). Clean The Dirty Filter And Impeller

In the first stage, you need to check and clean the filter and impeller which may be full of debris and dirt. Disconnect the filter from the cartridge counter. 

clean the  dirty filter

Then rinse and backwash the filter using a water hose as shown in the picture. Keep rinsing until the filter is completely dirt and debris free.

Next, inspect the impeller for any blockages.  Use a trim stick to remove debris inside the Impeller.

pull out the stuck debris from the impeller

Also, you can use a metal coat hanger, slightly bend at the end and then insert the wire slowly into the impeller. Pull out the stuck debris from the impeller.

ii). Clean The Blocked Pump’s Strainer Basket

Then, inspect the pump’s strainer basket.  Like a filter and impeller, it also might be blocked by debris and dirt. Unclog the strainer from the stuck debris and then allow the water to flow freely. 

iii). Low Water Level

The low water level is one of the most concerning facts for insufficient water flow. The water level for the pool heater should be halfway up the skimmer box. 

If the level is below the skimmer box, fill your pool water from the hose or from any water tank. It’s better to call professionals.

iv). Fix The Water Pressure Switch & External Bypass Valve Issue

The water pressure in the pool heater regulates the water flow to allow the normal operation of the heater. Thus, locate the switch from the In/Out header and ensure a correct voltage supply through it.

Besides, it is necessary to adjust the water pressure switch correctly. Don’t forget to check the placement of the bypass valves following the manual.

3. Corroded Unitherm Governor

Corroded unitherm governor is the third most suspecting factor in the case of the Rheem pool heater HL2 fault.

unitherm governor

This part of the heater regulates the water flow and helps to keep the water temperature completely perfect for swimming. 

Besides, it senses the water temperature and changes the function as needed to protect the essential heater parts from damage. 

Anyway, once the thermal governor is pitted, rusted, or corroded, it won’t regulate the water flow, and water will move very slowly. As a result, it picks up a lot of heat, which hits the high-limit switch.


This time, we will check the thermal governor for any corrosion:

To inspect the thermal governor, you need to disconnect the retainer plug. Remove the retainer plug from the inlet/Outlet Manifold. The UG will be held in place with a spring behind the plug. 

De-solder the older unitherm governor from the plug with a shaft of a long screwdriver. If it is corroded or rusted, be sure it is non-serviceable and the time comes to replace it. Replace the Unitherm Governor with the new one.

4. Faulty Internal Bypass Assembly

Along with the unitherm governor, the internal bypass assembly takes part in directing the flow of water. This is mainly a built-in internal automatic bypass valve, assembled in the In/Out header. 

The valve responds to changes in water pressure in the piping system and maintains a more constant volume of pressure through the heater system.

Due to a bad internal bypass valve, it won’t continue its normal operation and sends too much flow through the heat exchanger. For producing excessive heat inside the system, the HL switch trips and throws the HL2 fault.


Locate and inspect the internal bypass valve from the assembly. Detach the older bypass valve and check whether it is corroded or rusted. If yes, replace the corroded spring and internal bypass valve.

5. Defective Thermostat

Malfunctioning of the thermostat would be one of the leading reasons behind this.

If the thermostat won’t turn off at the set point and let the heater continually run, it would warm the heater more than normal.

Increasing temperature will lead to the pool heater HL2 fault problem.


You need to ensure that the thermostat is fitted properly and in well working condition. Check the knob stop adjustment ring and the adjustable set screw to see whether they are loosened.

Repair or replace the faulty thermostat. If there is no problem with the thermostat, readjust the temperature as bellows:

  • First, loosen the set screw adjusted with the knob stop adjustment ring
  • Then, rotate the knob stop ring and set it to your desired location.
  • Finally, tighten the set screw to confirm the set temperature.

6. Malfunctioning Of The Control Panel

A faulty control panel needs to be counted as the major reason when you are encountering an HL2 fault in your Rheem pool water heater.

rheem pool heater malfunctioning control panel

There is a touchpad on the control panel which allows you to select the desired pool temperature. 

But in case, if there is any internal circuit in the control panel, it will give faulty readings and cause a high limit 2 error problem. 


Contact a professional if you are suspecting the control panel is a culprit for this issue. He will better suggest whether you need to replace it or not.

6. Faulty High Limit Sensor

If all the above troubleshooting steps can’t resolve the HL2 error in your heater, it is sure that the high-limit switch is defective or has stopped operating. 

rheem pool heater faulty high limit sensor

Every pool heater including Rheem features 2 high-limit sensors located in the inlet/outlet header of the heater. See the picture below for a better understanding of the location:

The high limit 2 fault error code means the high limit 2 switch is faulty. There might be a bad or dirty connection at the switch or at times faulty wiring from the switch back to the board is responsible. Most of the time, the switch is defective. 


Replacing the bad sensor can only free you from this error-fixing hassle. Disassemble the bad sensor from the connection and install the new high-limit switch back in place. 

Tips From Expert:

In most cases, the area around the sensor gets unusually warm, which continually trips the sensor. To prevent this, experts suggest applying thermal paste or a heat shield above the high-limit sensor.  

It will effectively work as high temp insulation to the factory metal of the sensor. Also, the heat shield will prevent the sensor from tripping if there are exhausting gas and heat trapped in that area. 


What Does A High Limit Switch Do On A Pool Heater?

The high-limit switch is very crucial in a pool heater. It is used to spot when your water temperature has surpassed a secure level of 135 degrees Fahrenheit and instantly opens the heat exchanger outlet when that occurs.

How Long Does A Pool Heater Last?

Relying on the weather of the place you live in and what temperature you aim to heat your pool, different pool heaters can generally last anywhere between 6 to 12 years. If you properly maintain your swimming pool heater can even last more than 20 years.

Does A Gas Pool Heater Have A Pilot Light?

Yes! All the gas-powered pool heaters have a pilot light. But make sure that the pilot light is lit. It can easily keep going out by wind or water before heating the pool entirely.  

Final Say!

If you are encountering with Rheem pool heater high limit 2 fault problem, then worrying about it is obvious. To remove your worries, we have come up with 7 reasons behind this problem and their effective solutions in this article.

We are hopeful that now after knowing these reasons and solutions for the pool heater high limit 2 fault problem, you can solve this problem easily. 

Still, if this problem doesn’t solve or if any more help is required, then do let us know in the comment box. We will be very happy to help you and solve your problem ASAP.

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.

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