Rheem Tankless Water Heater Troubleshooting [7+ Easy Solutions]

The most common maintenance concerned Rheem Tankless electric water heater problems include:

  • The heater is not turning on.
  • Water is not getting hot enough or no hot water.
  • Too hot water.
  • The water is going cold after a few minutes.
  • And the Heater keeps turning off.

Plus, leaking water and strange sounds coming out from the system are the leading problems that often Rheem tankless users encounter.

rheem tankless electric water heater troubleshooting

Troubleshooting Tankless Water Heater Error Codes

Troubleshooting Tankless Water Heat...
Troubleshooting Tankless Water Heater Error Codes

While troubleshooting, you need to look for major signs to identify the reasons behind the issue. Then, you have to fix the troubles based on the reasons. But to do so precisely, the need for a well-proven solving guide is obvious. 

Go on reading our extensive Rheem tankless water heater troubleshooting guide to breaking down each of the problems efficiently.

Rheem Tankless Water Heater Troubleshooting [7 Easy Solutions]

Here are the details of all major Rheem tankless heater problems, explained with their quick solutions. Let’s start:

1. Water Heater Won’t Turn On

It is a common phenomenon that you may experience a restricted-energy supply to your water heater. There are a few reasons why your Rheem tankless water heater won’t power on

water heater won't turn on

Either the energy supply is cut off or the circuit breaker has tripped. At times, it could be a simple issue like a blown fuse on the outlet or having any loose wire in the connections. 

If all these are not related in this case, we bet that the inside water flow sensor is not working properly, causing the circuit board not to turn on. Here is the below picture indication of the flow sensor:

electric water heater flow sensor

How To Fix

Here is all how you will deal when your Rheem tankless electric water heater won’t turn on:

  • First, check the main electrical panel of your house. Look for any obstruction, causing the circuit breaker to trip. Remove it. Then reset the breaker to get back your heater in operation.
  • In case it is a blown fuse, be quicker to replace it. Then check and find if there is any loose wire. Tighten or replace the worn-out one.
  • If all these fail to restart the heater, you need to inspect the heater inside and check the flow sensor. Contact a professional to replace the defective sensor.

2. Water Is Not Getting Hot Enough Or No Hot Water

If your electric water heater isn’t not getting the hot water you desire, there’s a good chance that you have set the temperature too low. If not that so, the heater might be reaching the limit.

Basically, there is a limit switch in the heater, which helps to keep the temperature at an appropriate level. 

water is not getting hot enough

Now in case the high limit switch is tripping or wearing out at some point, it will switch off the heater function. Other major reasons why there is a problem in heating the water include:

  • Bad heating element.
  • Tripped circuit breaker.
  • Running too many appliances at once.
  • High water flow rate.
  • Incorrect or loosened wiring.
  • Internal part failure or mixing too much cold water.

No worry! Fix the below well-proven procedures to solve the matter quite easily.

How To Fix

First, do the easy fix by turning up the temperature on the thermostat. If you already do so, figure out the reason for tripping the high-limit switch. Do a quick reset in this case by turning off the breaker to the unit. 

Besides, make sure the breakers at the main electrical panel are ON and in working order. Then look for any damages or loose wiring going through the unit. Fix that fast.

To ensure the optimal temperature output, there should be a maximum flow rate on your heater.

A tankless water heater activation flow is approximately 0.3 GPM (1.1 LPM). Check the flow rate on your heater through a flow regulator and reduce the level if it is too high. 

Still, there is no hot water, it is time to check the heating elements. De-assemble your heater and find the heating elements as indicated below.

These elements are designed for 240 volts. In case of a lower voltage, they produce less heating power. Replace the bad ones.

Make sure that too much cold water is not mixing with hot water. You may install an anti-scald guide on your faucet to reduce the amount of cold water mixed.

3. Water Is Getting Too Hot

If the outcome water from the water heater is too hot, setting the thermostat too high is the most probable fact that users often make mistakes. But in case that is not so, the water flow rate from the heater is bet too low. 

 water is getting too hot

In most cases, due to a faulty thermostat, or failing heating elements, the heater fails to maintain the temperature at an adequate level. 

Plus, the loosened temperature at the connection point or at times the defective sensor is the culprit. 

How To Fix

There is nothing to worry about! By following the few quicker steps, you can minimize the high-temperature issue of your water heater.

First off, check the thermostat setting and set the level low if it is too high. Set the thermostat to around 120 F. 

Then, check for any loose and damaged wiring from the heater. Do a quick replacement of the worn-out wiring. Monitor the thermostat as well and ensure it is in well-working order. 

Don’t miss to check the water flow. If it is not at the recommended level, open the valve a bit more to increase the pressure.

If all the above methods have been ruled out, disconnect the front panel and inspect the heating elements. We are pretty much sure that the elements are defective and you need to replace them as soon as possible. 

Look through the temperature sensor as well and ensure it is tightened at its connection. Replace the faulty sensor to stop the heater from overheating. We suggest you contact a professional to perform this task.

4. Heater Goes Cold After A Few Minutes

It is the most often happening issue that your heater water suddenly gets cold after a few minutes.

The fact is known as a cold water sandwich and a few major raps might be counted as the culprit for this issue. A broken flow sensor is the major one of them.  

heater goes cold after a few minutes

A flow sensor is used to measure the water entering your system and through which it sends signals to the unit’s control board.

In the case of a bad sensor, fluctuation in the temperature is obvious as it is failing to sense the water flow. 

Plus plumbing crossover and low Water Pressure are also the most probable reasons why your tankless water heater is running hot and cold.

How To Fix

First, check if your system is running through low water pressure. If the flow rate is lower than the activation flow rate required, it results in the control board stopping heating the water.

In this case, check if the valve is partially closed, or not open. Head to the valve and open it up all the way. 

Next, remove the front panel and inspect the flow sensor to see whether it is broken. Replace the faulty flow sensor with the assistance of any professional.

Thirdly, plumbing crossover can also cause the issue which happens due to a faulty mixing valve or damaged plumbing. To fix this situation, you need to inspect the mixing valve and change the cartridge. 

5. Heater Keeps Shutting Off

If your electric water heater is failing to stay on, be sure you are encountering a power supply interruption. Either it is a simple loose wire or might be a circuit breaker problem. 

rheem heater keeps shutting off

Plus, the low water flow rate through the unit and the faulty thermostat are the major reasons in this case. Most of the time, it happens due to internal mechanical defects or clogged filter screens. 

The greater chance is the heating element is failing but continuing heating the water even if the thermostat does not direct. This increases the heater temperature which trips the high limit switch, leading to turning off the power.

How To Fix

Here are some effective ways to diminish the heater trouble that is turning off constantly:

  • First off, check all the wiring connections going through your heater and fix the loose ones. If it is a circuit breaker issue, reset the breaker.
  • Then monitor that your heater is ensuring the minimum water flow requirements. If not, fix the water flow issue.
  • Examine the thermostat function to see whether it is in good operation or not. Replace the bad thermostat. 
  • There is a built-in filter screen in your heater at the inlet connection which needs to be cleaned.
  • Inspect the heating elements. Call a professional if you are suspecting bad elements. 

6. Water Heater Leaking

Your tankless water heater may leak for any of the following reasons:

water heater leaking
  • Sediment or mineral buildup inside the system from hard water.
  • Blocked pipes.
  • Weak pipe connections.
  • Too-high water flow.
  • Bad water conditions.
  • Improper installation of the heater.

How To Fix

First off, check for any bad pipe connection. All tankless water heaters are equipped with a relief valve that is more prone to leakages. Inspect the pipes jointing, fix the loosened one, and ensure that the valve is well tightened. 

Secondly, examine the inlet and outlet pipes for any blockages. Clean the pipes properly.

Next, check the water pH whether it is too much or in level. Because more acidic water creates pinholes in your piping and causes leaks. As a solution, you can install an acid neutralizer on your household plumbing system. 

Then, ensure that the flow water rate of your unit is at the recommended level. If it is too high, reduce the flow by adjusting the valve. Must drain or flush the system if there is any sedimentation build-up. 

7. Heater Is Making Noise

If you are hearing a strange noise while starting and heating the water, be sure your heater is going through some major malfunctions. Most often, it is likely related to heater overheating due to sediment build-up on the heating elements. 

 rheem tankless water heater is making noise

While heating, the heater pipes come in contact with hard water minerals like calcium and magnesium. After a long time, these minerals form into hard particles and clog the pipes.

Whatever the fact is, you need to descale or flush your tankless water heater to reduce the annoying sound.

How To Flush Rheem Tankless Water Heater

Follow the below step-by-step procedures to flush out your tankless water heater:

Step 1: First off, shut off the electrical power of your heater and close the water shut-off valve as well. Open the faucet to drain the remaining water from the heater. Then close the hot water shut-off valve.

Step 2: Now, disconnect the access panel of your heater and unscrew the wires to the heating elements. This time, you have to disassemble the heating elements. Just turn on the hexagonal brass top in a counter-clockwise direction. 

Step 3: Place the heating elements in the copper chambers. Now, fill the chamber with the solution of vinegar and water to remove the scale. Avoid chemical solutions of any kind. Let it sit for about 1-2 hours to break up the scale on the elements.

Step 4: Drain the cleaning solution and install the heating elements back in place. Secure all the wires of the elements. 

Step 5: Now remove the cold water inlet filter from the inlet connection. Clean the filter as well under a cold tap and replace it securely.

Step 6: Once all are done, turn on the hot & cold water shut-off valves. Place the access panel and turn on the power supply.

Scale Build-Up Prevention Tips

  • We recommend flushing your water heater once or twice a year if you are living in hard water areas. 
  • It will be better to install a water softener or water treatment device to maintain the optimal performance of your water heater. 
  • You should always be aware of the water condition that is running through your plumbing system. It should meet the below recommendation: 
TDSUp to 500 mg/L
CO2Up to 500 mg/L
Total hardnessUp to 200 mg/L
Aluminum0.05-0.2 mg/L
ChlorideUp to 250 mg/L
CopperUp to 1.0 mg/L
IronUp to 0.3 mg/L

How To Reset Rheem Tankless Water Heater

Resetting a tankless water heater is quite straightforward and can be done by following the quick steps. Here are the step-by-step procedures to perform a reset on your Rheem tankless unit:

Step 1: First off, locate the reset button on your water heater. Most probably, you will find it on the side or front of the unit.

Step 2: Press the rest button firmly once to take it into “Reset Mode.” It is quite necessary to start up the water heating process again.

Step 3: Wait ten seconds to let the unit complete the resetting procedures. When done, the red light will turn green, indicating that the heater has tuned into the default setting.


What is system overload in a tankless water heater?

When too many appliances are running simultaneously through a single heater, it exceeds the heater’s capacity. If this happens, the heater stops heating water and leads to system failure. This situation is known as system overload.

Do electric tankless water heaters need to be vented?

In a short answer: No! The electric tankless heater uses electric burners to heat water. As there is no chance of fuel burning, that is why it doesn’t require venting, unlike a gas or propane heater.

Wrapping Up!

Tankless electric heaters are highly efficient in heating water on demand. It is also quite common that several problems may arise while operating that stop the heater from functioning in a mannered way. 

That’s the point users get in trouble and start looking for reasons for that issue. The case is also the same for the Rheem model. That’s why we have decorated the Rheem tankless electric water heater troubleshooting guide. 

Hope that it was an informative read for you and that now you can fix any of the heater issues with ease.  Don’t miss sharing your thoughts and feedback through comments. We will feel glad to see you here!

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