Rheem Tankless Water Heater Troubleshooting [Complete Guide] (2023)

Some of the most common maintenance issues with Rheem electric water heaters include:

  • The heater does not turn on.
  • The water does not get hot enough or there is no hot water.
  • Water too hot.
  • The water will cool down after a few minutes.
  • The heating keeps going off.
  • And how to fix the most common Rheem water heater error codes.

Also, water leaks and strange noises coming from the system are the main problems that Rheem Tankless users often encounter.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (1)

When troubleshooting, you should look for important signs to identify the causes of the problem. Then you need to fix the problems based on the reasons. But to do this accurately, the need for a proven solution guide is evident.

Keep reading our detailed Rheem water heater troubleshooting guide to solve each of the problems efficiently.

table of Contents

  • Rheem Water Heater Troubleshooting Guide [A Complete Guide]
  • 1. The heater cannot be turned on
  • 2. The water is not hot enough or there is no hot water
  • 3. The water gets too hot
  • 4. The heater cools down after a few minutes.
  • 5. Heater keeps turning off
  • 6. Water heater leaks
  • 7. The heater is noisy
  • Troubleshooting the most common error codes for Rheem water heaters
  • How to Reset Your Rheem Electric Water Heater
  • Frequent questions:
  • What is a system overload on a water heater?
  • Do electric instantaneous water heaters need venting?
  • ¡Diploma!

Rheem Water Heater Troubleshooting Guide [A Complete Guide]

Here are the details of all the major Rheem no flow heater problems, explained with their quick fixes. Let us begin:

1.Can't turn on the heating

It is a common phenomenon that your water heater has limited power supply. There are a couple of reasonsWhy won't your Rheem water heater turn on?.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (2)

Power has been interrupted or the circuit breaker has tripped. Sometimes it can be a simple problem, like a blown fuse in the outlet or a loose wire in the connectors.

If all this is not related in this case, we bet that the internal water flow sensor is not working correctly, causing the plate not to turn on. Here is the following flow sensor display picture:

Troubleshooting tankless water heating...

Troubleshoot Error Codes for Instant Water Heaters

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (3)

how to repair

Here's what to do if your Rheem electric water heater won't turn on:

  • First, check the main electrical panel in your house. Look for obstructions that could cause the breaker to trip. remove it. Then reset the breaker to get your heater working again.
  • If it's a blown fuse, replace it faster. Then check for a loose wire. Tighten or replace the worn one.
  • If all of this doesn't reset the heater, you should inspect the inside of the heater and check the flow sensor. Contact a professional to replace the faulty sensor.

2.The water does not get hot enough or there is no hot water

And youThe electric water heater is not receiving hot waterYou want, there's a good chance you set the temperature too low. Otherwise, the heater could reach its limits.

Basically, there is a limit switch on the heater that helps keep the temperature at a reasonable level.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (4)

If the upper limit switch trips or wears out at any time, it turns off the heating function. Other main reasons for a problem with water heating are:

(Video) Rheem Tankless Hot Water Tank | Troubleshooting

  • Bad heating element.
  • Circuit breaker tripped.
  • Running too many devices at the same time.
  • High water flow.
  • Incorrect or loose wiring.
  • Internal parts failure or too much cold water mix.

No problem! Please fix the following best practices to resolve the issue easily.

how to repair

First, do the easy fix by raising the temperature on the thermostat. If you have already done this, find out what caused the high limit switch to trip. In this case, perform a quick reset by turning off the breaker of the device.

Also make sure the circuit breakers in the main electrical panel are on and operational. Then look for any damage or loose cables running through the device. Fix that quick.

To ensure optimum temperature output, your heater must have a maximum flow rate.

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

Still no hot water, time to check the heating elements. Disassemble your heater and locate the heating elements as indicated below.

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

Take care not to mix too much cold water with hot water. You can install an anti-scald guide on your faucet to reduce the amount of mixed cold water.

3. The water gets too hot

When the water coming out of the water heater is too hot, setting the thermostat too high is the most likely occurrence that users often make mistakes. However, if this is not the case, the water flow from the heater is too low.

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In most cases, the heater is unable to maintain the temperature at a proper level due to a faulty thermostat or heating elements.

Also loose junction temperature or sometimes bad sensor is to blame.

how to repair

There is nothing to worry about! By following the quickest few steps, you can minimize your water heater's high temperature problem.

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

Then check for loose or damaged wires from the heater. Make a quick replacement of worn wiring. Also check the thermostat and make sure it is in good condition.

Don't forget to check the water flow. If it is not at the recommended level, open the valve a little more to increase the pressure.

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

Also look through the temperature sensor and make sure it is tight in its connector. Replace the faulty sensor to prevent the heater from overheating. We recommend that you contact a professional with this task.

4.The heater cools down after a few minutes

The most common problem is that the heating water suddenly becomes cold after a few minutes.

The occurrence is known as a cold water sandwich, and a few big hits could be counted as culprits for this issue. A broken flow sensor is the most important of them.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (6)

A flow sensor measures the water entering your system and sends signals to the unit's control board.

(Video) Rheem Tankless water heaters troubleshooting

In the case of a bad sensor, a temperature variation will be evident as the flow of water will not be detected.

Additionally, plumbing and low water pressure are also the most likely reasons why your water heater is running hot and cold.

how to repair

First, check if your system is running with low water pressure. If the flow is less than the required trigger flow, it will cause the control board to stop heating the water.

In this case, check whether the valve is partially closed or not open. Go to the valve and open it fully.

Then remove the front panel and check the flow sensor to see if it is damaged. Replace the faulty flow sensor with the help of a specialist.

Thirdly, the crossing of the pipes can also cause the problem that arises from a faulty mixing valve or damaged pipes. To fix this situation, you need to check the mixing valve and change the cartridge.

5.The heater keeps turning off

If your electric water heater won't stay on, be sure to find a power interruption. It's just a loose wire or a problem with the circuit breaker.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (7)

Also, low water flow through the device and faulty thermostat are the main reasons in this case. Most often this happens due to internal mechanical defects or clogged screen filters.

Most likely the heating element is failing but the water continues to heat even when the thermostat is not controlling. This increases the temperature of the heater, which activates the high limit switch and causes a power outage.

how to repair

Here are some effective ways to reduce heater problems that keep going off:

  • First, check all the wire connections that go through your heater and repair any that are loose. If it is a breaker problem, please reset the breaker.
  • Then check that your heater meets the minimum water flow requirements. If not, fix the water flow issue.
  • Examine the function of the thermostat to see if it works well or not. Replace faulty thermostat.
  • Your heater has a filter screen built into the inlet connection that must be cleaned.
  • Check heating elements. Call a professional if you suspect defective items.

6.water heater leak

Your instantaneous water heater may be leaking for one of the following reasons:

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  • Sludge or mineral deposits in the system due to hard water.
  • clogged pipes.
  • Weak pipe connections.
  • Water flow too high.
  • Bad water conditions.
  • Improper heater installation.

how to repair

First, check for a bad pipe connection. All instantaneous water heaters are equipped with a relief valve, which is more prone to leakage. Check pipe connections, repair loose ones and make sure valve is tight.

Second, inspect the inlet and outlet pipes for blockages. Clean the pipes properly.

Then check the pH of the water to see if it is too high or balanced. Because more acidic water creates holes in the pipes and causes leaks. As a solution, you canInstall an acid neutralizerin your home installation system.

Then make sure that the water flow from your device is at the recommended level. If it is too high, reduce the flow by adjusting the valve. If there are deposits, the system should be emptied or flushed.

7.The heater is noisy

If you hear a strange sound when turning on and heating your water, make sure your heater is seriously faulty. In most cases this is probably related to the heater overheating due to deposits on the heating elements.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (9)

During heating, the heating pipes come into contact with hard water minerals such as calcium and magnesium. These minerals form hard particles after a long time and clog pipes.

Whatever the fact, you should decalcify or flush your water heater to reduce annoying noise.

How to Flush Rheem Water Heater

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

(Video) How To Reset Your Tankless Water Heater

Paso 1:First, turn off the power to your heater and also turn off the water shutoff valve. Open the faucet to drain the remaining water from the heater. Then close the hot water shutoff valve.

Paso 2:Now disconnect the access cover from your heater and unscrew the wires going to the heating elements. This time you need to disassemble the heating elements. Simply turn the brass hex top counter-clockwise.

Paso 3:Place the heating elements in the copper chambers. Now fill the chamber with the vinegar and water solution to remove scale. Avoid chemical solutions of any kind, leave it to act for around 1-2 hours to dissolve the limescale from the elements.

Stage 4:Drain the cleaning solution and reinstall the heating elements. Secure all wires from the elements.

Paso 5:Now remove the cold water inlet filter from the inlet connection. Also clean the filter with cold water and replace it safely.

Paso 6:When everything is ready, open the hot and cold water shutoff valves. Install the access panel and turn on the power.

Tips to avoid lime deposits

  • We recommend flushing your water heater once or twice a year if you live in hard water areas.
  • It is best to install a water softener or water treatment device to keep your water heater running at its best.
  • You should always be aware of the conditions of the water flowing through your plumbing system. You must comply with the following recommendation:
TDSUp to 500mg/l
CO2Up to 500mg/l
absolute hardnessUp to 200mg/l
Aluminum0,05–0,2 mg/l
ChlorideUp to 250mg/l
copperUp to 1.0mg/L
EisenUp to 0.3mg/l

More commonRheem Water Heater Error CodesTroubleshooting

All Rheem instantaneous water heaters have a built-in electronic diagnostic system. When the heater goes through various malfunctions, it will display an error on the LED display or on the control panel in the form of a code.

Resetting the heater is an effective system reset process to clear the code. Helps get the heater back to normal operation after faults have been rectified.

In any case, if you can't fix your error code even after rebooting the system, you need to find out the exact specification of the error. Then you need to find out the possible reasons behind the error along with the solution.

Let us track down some important Rheem water heater error codes and fix the problem efficiently:

01. Error code 00

The Rheem water heater "error code 00" on the display indicates that your water heater has been running continuously for more than an hour.

how to repair:

Reset the device using one of the two methods above. If a circulation pump is installed with the heater, remove or turn it off as well.

02error code 10

Error code 10 on the front panel means that the flame has been lost approximately 8 times.

how to repair:

Please reboot the device first to clear the code. If the error persists, there are a few things you need to fix:

  • Monitor the gas pressure of your instantaneous water heater during operation.
  • Be sure to securely connect the wire of the gas valve and the flame detection sensor. Also check the correct connection of the ignition transformer.
  • Clean the spark igniter with steel wool or replace if necessary.
  • If you still get the same error, replace the circuit board.

03. Error code 11

when you seeRheem water heater with error code 11Please make sure your water heater has failed ignition process about 10 times.

Simply resetting the heater will clear the fault. If not, follow the troubleshooting steps below:

how to repair:

First, make sure the system gas pressure is between 5.0″ W.C. and 13.0″ W.C (1.25 to 3.24 kPa). Also make sure that the gas valve connection is secure.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (10)

Check that the ignition transformer and flame detection sensor are connected correctly.

Sand the spark igniter with steel wool or sandpaper to remove any oxides. Replace damaged igniter.

04. Error code 20

Error code 20 on the front panel is a clear indication that the high limit thermal switch is normally closed and open when it fails.

how to repair:

  • Reset the water heater to clear the error.
  • If that fails, check the high limit switch and make sure the connection is proper.
  • Measure the resistance of the switch. Replace the switch if the resistance indicates zero.

05. Error code 21

Error code 21 on the Rheem instantaneous water heater is the error that the heat exchanger outlet temperature is too low. This is mainly due to a clogged heat exchanger. Other important reasons are:

(Video) Homeowner's Guide, how to unlock a Rheem tankless water heater

  • Clogged air inlet filter.
  • Plug in the neutralizer.
  • Clogged condensate drain system.
  • faulty circuit board

How to fix:

The first step is to descale the carbon deposits from the heat exchanger. You can do this by flushing and draining your hot water heater. Also check the continuity of the heat exchanger thermistor. It should read between 0.8 and 20k ohms.

Clean the clogged air intake filter. Also check the neutralizer for corrosion. Replace if necessary. In most cases, the error occurs due to a blockage in the condensate drain system, which must be cleaned. Wondering how to do that? go to ourDetailed Guide On How To Deal With Error Code 29 On Rheem Water Heater.

06. Error code 29

Rheem error code 29 indicates that the heat exchanger temperature is too low or that the neutralizer in the condensing unit is clogged.

How to fix:

Follow these simple steps to fix this problem:

Paso 1:Clean the fins of the heat exchanger. Also clean the air intake grill.

Paso 2:Make sure the connection between the APS/condensate and the main controller is secure. Check hose connection to APS/condensate.

Rheem Tankless Water Heater Troubleshooting [Complete Guide] (11)

Paso 3:Clear condensate line and drain clogs.

Stage 4:Replace the condensate neutralizer.

07. Error code 41

The error code tells users that the fan speed is too high when the flame is on. Unlike others, try to clear the code by rebooting the device. If it turns out that it is not good, please do the following troubleshooting procedure:

how to repair:

  • Clear any obstructions from the vent port.
  • Inspect the burner assembly and make sure it is in good condition.
  • Next, check the operation of the fan. If you find that the fan speed is too low or too high, you should replace the fan.

08Error code 43

If the burner overheat switch opens, the heater will display error code 43 on the front display. The error indicates that a system reboot is required. If you still have the same code, follow the section below for more solutions:

how to repair:

  • Check burner overheat switch connections and make sure they are all secure.
  • Also measure the resistance of the switch. Replace the switch if the reading is zero.

09. Error code P1

The Rheem water heater P1 error code primarily indicates that the water flow from the device is too low. Clogged air intake filters, faulty flow sensors, sediment buildup in the heater, and clogged aerators are some of the main reasons for this code. Also, using too small a water heater will cause the P1 error code.

How to fix:

  • As a first step, inspect and clean your faucet aerators. Also clean the water filter screen.
  • Inspect the water flow sensor for defects. Replace if necessary.
  • Look for corrosion in the pipes in your house.
  • If you suspect that sediment has built up in the heater, you should flush the water heater.
  • Also make sure you are not using a tankless water heater that is too small. If you're not sure which size water heater is right for your home's hot water needs, you can check out our detailed discussion in this guide.How To Fix Rheem Tankless Water P1 Error Code.

How to Reset Your Rheem Electric Water Heater

As you already know, resetting your Rheem tankless water will correct most error codes that appear on the heater gauge. Here is the easy method and steps to reset your Rheem water heater:

Paso 1:First, turn off all hot water faucets connected to your Rheem water heater.

Paso 2:Now turn off power to your tankless system. Turn off the device from the control panel.

Paso 3:Then disconnect the cable from the power connector.

Stage 4:Leave the device unplugged for about 10-15 minutes and then plug it back in. The reboot is done.

Alternatively, there is another simple method. To learn this method, you can read ours.Complete guide on why and how to restart your Rheem water heater.

Frequent questions:

What is a system overload on a water heater?

Running too many devices through a single heater at the same time will exceed the capacity of the heater. In this case, the heater stops heating the water and causes a failure in the system. This situation is called system overload.

Do electric instantaneous water heaters need venting?

In a short answer: No! The electric water heater uses electric burners to heat the water. Because there is no chance of burning fuel, unlike a gas or propane heater, there is no need to vent it.


Tankless water heaters are highly efficient at heating water on demand. It is also quite common for various problems to arise during operation that prevent the heater from working properly.

That is the point where users get into trouble and start looking for the reasons behind this issue. The case is also the same for the Rheem model. That is why we have created the Rheem Continuous Flow Electric Water Heater Troubleshooting Guide.

(Video) Man Tips: Troubleshooting Rheem Tankless Hot Water Heater

I hope you found it informative and can now fix any heating problem with ease. Feel free to share your thoughts and feedback in the comments. We are happy to see you here!


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