Rheem Tankless Water Heater Code 29 (How to Troubleshoot)

Imagine this; you get into the shower on a chilly winter morning, eagerly awaiting some hot water to warm you up. But instead of a steady stream of steamy water, you get ice-cold water that numbs your nerves. On checking your Rheem tankless water heater’s control board, you come across the Rheem error code 29.

The Rheem tankless water heater code 29 may be caused by a low heat exchanger outlet temperature, a clogged neutralizer, a blocked heat exchanger, or a faulty PCB. Solutions include increasing the heat exchanger’s outlet temperature and unblocking the heat exchanger.

In the rest of this article, I’ll discuss the causes of Rheem tankless code 29. I’ll also discuss fixing each issue to restore the heater’s normal function. Keep reading!

1. Low Heat Exchanger Outlet Temperature 

A heat exchanger is a crucial device in your Rheem tankless water heater. It allows the hotter fluid to interact with the colder fluid without mixing them. Thus, the heat exchanger transfers the gas burner’s heat to the water passing through it.

If the temperature at the heat exchanger’s outlet is too low, it could cause the Rheem tankless water heater to show error code 29. In this case, the error code indicates that the water outlet temperature is too low, which is why you get cold water in your shower or any outlet point.

How To Fix

Fixing this problem entails adjusting the heat exchanger’s outlet temperature manually. Here is how to do it:

  1. Open the breaker panel and turn off the heater’s breaker.
  2. Remove the access cover on the heater’s side by unscrewing the screws.
  3. Locate the thermostat dial.
  4. Insert a flat-head screwdriver through the thermostat dial.
  5. Rotate the thermostat to achieve your desired water outlet temperature.
  6. Replace the access cover and turn on the breaker.

2. A Clogged Neutralizer Is Causing Rheem Tankless Code 29

The Rheem tankless water heater has a neutralizer, a device that prevents corrosion within the unit by filtering out acidic water. 

Rheem tankless water heater neutralizer

Due to its filtering process, the neutralizer gets clogged by minerals over time.

When the neutralizer gets clogged, it restricts the water flow and can trigger the rheem tankless water heater error code 29. In this case, the water won’t reach its desired temperature before exiting through the outlet.

How To Fix

To fix this issue, you need to clean or replace the neutralizer. Here is how:

  1. It’s best to turn off the heater’s power supply by flipping off its breaker in the panel.
  2. Unscrew the screw holding the access cover in place to remove it.
  3. Locate and disconnect the neutralizer from its tubing using pliers.
  4. Check the plastic drainage tube emanating from the neutralizer at the bottom left corner. Remove the valve on this tube to drain the water.
  5. Clean or replace the neutralizer and reconnect it to the tubing. Ensure all connections are secure.
  6. Replace the access cover and turn on the breaker.

3. A Blocked Heat Exchanger Is Behind the Code 29 Error

The heat exchanger in a Rheem tankless water heater can get clogged by mineral deposits over time. The scale build-up in the heat exchanger impairs the regular water heating operation of the heater. When this happens, the dirt prevents the heat exchanger from exchanging the heat efficiently, leading to cold water when it should be hot.

This issue may cause the Rheem error code 29 because the water can’t reach its desired temperature before being released through the outlet.

The heater’s remote control should confirm if the error is due to a blocked heat exchanger. Check the remote control for a “Maintenance information ’4y’” display. This display will confirm that the error code 29 on your Rheem water heater is due to a blocked heat exchanger.

How To Fix

Inspecting your heater’s heat exchanger for scale build-ups or restrictions would be best. If you find any, clean them and flush the system. 

Make sure to refer to the Rheem water heater’s manual for specific instructions on how to clean the heat exchanger. It may also require special tools, so make sure you have them before starting the cleaning process. 

Alternatively, you can opt to hire a professional plumber for this task.

Here is a video that demonstrates how to clean a heat exchanger:

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4. A Defective PCB Is Causing the Rheem Error Code 29

A Printer Circuit Board (PCB) is responsible for controlling and regulating the operation of a Rheem tankless water heater. The PCB can get damaged over time for various reasons, such as power surges or malfunctions in other components.

The PCB can cause the Rheem error code 29 if it’s faulty because it affects the temperature control in the heat exchanger.

By measuring the heat exchanger thermistor’s resistance, you can determine if the error is due to a defective PCB.

A standard heat exchanger thermistor’s resistance, between 4,000 and 10,000 ohms with the error code 29, confirms that the PCB is defective.

How To Fix

The solution to this problem is to replace the PCB. Here’s how:

  1. Open the breaker panel and flip off the breaker to turn off the power supply to the heater.
  2. Unscrew the four screws on the front panel and pull it out.
  3. Locate the Printer Circuit Board and unscrew the screws.
  4. Remove the multi-pin connectors from the old PCB.
  5. Lift the old PCB gently and remove it from the assembly.
  6. Install the new PCB in position and attach the multi-pin connectors.
  7. Securely screw in the new PCB and replace the front panel.
  8. Turn on the power supply by flipping the breaker and check if you have resolved the error code.

It’s important to note that replacing a defective PCB can be pretty complicated for those unfamiliar with water heater components and their functions. Therefore, it’s best to hire a professional for this job to ensure they do it correctly—to prevent further damage to the heater.

replacing defective PCB

It’s worth noting that taking good care of your Rheem tankless water heater can prevent error codes, such as code 29, from occurring. You can achieve this by regularly cleaning and flushing the system to prevent mineral deposits from building up in the heat exchanger.


Rheem code 29 error indicates that the heater has an issue that needs your attention. This error is mainly due to a blocked heat exchanger. Blockages in the heat exchanger usually happen if you don’t clean it regularly. Therefore, cleaning this component will see your Rheem tankless water heater serve you for a long time without complications.