Rheem Tankless Water Heater Code 29 [Why+ How To Fix]

Rheem tankless water heater code 29 is the error indicating that the heat exchangers outlet temperature is too low. Corrosion buildup in the heat exchangers is the root reason for this error. 

But that’s not the end! Other major reasons include:

  • The heat exchanger thermistor is out of normal resistance.
  • Blocked air intake filter.
  • Clogged in the neutralizer.
  • Blockage or incorrect installation of the condensate drainage system.
  • And, defective PCB. 
rheem tankless water heater code 29

Start troubleshooting by cleaning up the shoot and dirt from the heat exchanger fins. For this, you have to flush your water heater with the proper method. Wondering how to do so? Get into our comprehensive guide to learn the details.

Quick Solutions For Rheem Tankless Water Heater Code 29

Before moving to the detailing parts, it will be worth having a quick glimpse at the below table, highlighting all the probable reasons with proper fixes:

Probable ReasonsPossible Solutions
Corroded heat exchanger> Flush and drain your tankless water heater.
Abnormal resistance reading of the heat exchanger thermistor> Measure the thermistor resistance.
> Replace the damaged one. 
Clogged air intake filter> Clean the air intake filter. 
Rheem tankless water heater neutralizer clogged> Drain the water from the drain line through neutralizers to remove the clog.
> If needed, replace the faulty neutralizer. 
Blocked condensate drainage system> Clean out the drainage pipe. 
Incorrect installing the drain pipe> Ensure the correct fitting of the condensate drain line. 
Defective PCB> Replace the bad PCB

How To Fix Error Code 29 on Rheem Tankless Water Heater [7 Easy Solutions]

Now, get to the details of solving procedures to erase the error code 29 on the tankless water heater: 

Note: You can also read how to fix Rheem tankless water heater code 12.

1. Corroded Heat Exchanger

Behind the error code 29 on the Rheem tankless water heater, the blocked heat exchanger is the root culprit to blame. If you notice low temperature from the water heater, higher chances are the heat exchanger gets blocked from the deposits. The most common cause of these deposits is the minerals from the hard water.

Basically, a tankless water heater uses heat exchangers having small passageways consisting of parallel plates or tubes. When you are turning on the hot water faucets, the incoming water passes through the heater exchangers which raises the water temperature. 

After long use, building up hard minerals from water on the passageways is quite obvious. The deposits lower the exchanger’s efficiency and throw the error code 29. 

In this step, you have to inspect and descale your water hearer exchangers. Let’s go into the below section to learn the processes.

How To Clean Rheem Tankless Water Heater Heat Exchanger?

To descale the carbon buildup from the heat exchanger, you need to drain and flush your complete system. Follow the below few phases to do so:

Phase #1: Turn off isolation valves and gas

As for the first step, turn off the isolation water valves connected to your water heater. You will find a blue inlet valve and a red outlet valve to the connection. Just turn the levers to the perpendicular position of the pipe.

Phase #2: Connect The Hoses

In this step, you will need two sturdy water hoses. Connect the hoses to the blue inlet and red outlet valves. Ensure a secure and water-tight connection of the hoses to the valves with pliers.

connect the hoses

Phase #3: Attach The Hoses To The Circulation Pump

Now you will need a circulation pump. If you have a water heater flushing kit, you will get a pump with the kit. Anyway, connect the other end of the hoses with the circulation pump and discharge it into the bucket.

attach the hoses to the circulation pump

Phase #4: Add Cleaning Agent

Now add a cleaning agent to the bucket. If you don’t have a cleaner, you can use vinegar. 

Open the inlet and outlet valves and let the chemical water circulate through the heater for about 45 minutes to one hour.

Phase #5: Flush Out The Cleaning Agent

After the time has passed, stop the circulation by turning off the agent. Turn off both valves and detach the blue inlet valve hose. 

flush out the cleaning agent

To flush out the remaining cleaning agent or vinegar, turn on the cold water inlet valve and flush out everything through the hot water side.

 Let it continue for 5 to 10 minutes. Then reassemble everything. 

2. Heat Exchanger Thermistor Resistance Is Out Of Range

After flushing the water heater and still there is the same code on the display, higher chances are the heat exchanger thermistor is going through abnormal resistance.

heat exchanger thermistor resistance is out of range

So it’s better to inspect and check the resistance readings of the thermistor to determine its defection. If you are wondering how to do so, just follow the below section.

How To Do:

First up, turn off the power supply to your water heater. Remove the front panel to access the heat exchanger assembly. Now locate the thermistor from the heat exchanger outgoing path. If you are confused, look at the above picture.

Take a multimeter and set it to the Ohm setting.  before measuring the resistance of the thermistor, don’t forget to remove the connector of the PCB. 

Connect the probes to red wires. A well-working heat exchanger thermistor should give a reading between 0.8 to 20k ohm.

If the reading is not in this, it is sure that the thermistor is at fault. You need to replace the bad thermistor to get the heat exchanger back in operation. We recommend contacting a professional to handle the replacement tasks for you.

3. Clogged Air Intake Filter

Incomplete combustion is another root reason for occurring trouble code 29 on the tankless water heater. This mainly occurs due to plugging up the air intake filter. The air intake filter is an essential filter of the tankless system that keeps the bugs and dirt out of your system. 

clogged air intake filter

As it is always in the contract of grim, thus getting dust and being blocked is quite obvious. That’s the point, the airflow gets slow and the combustible air enters the system. 

Due to a lack of combustion air, the heat exchanger can’t able to exchange the heat and causing error 29 on the display. 

 If this is the case, cleaning the clogged air intake is the only solution.

How To Clean Air Intake Filter In Rheem Tankless Water Heater?

Here are simple procedures to clean the air intake filter:

  • First, turn off the power supply to your water heater. It is the first safety measure that you need to follow before cleaning. 
  • Then remove the front cover plate by unscrewing all the nuts and bolts.
  • Once done, locate the air intake filter from the top right corner of the inside chamber. We have already indicated this in the above picture.
  • The filter will be secured in place with a screw. Unscrew it and pull the filter towards you.
  • Take it under the running water and clean the stuck grime and dirt. If needed, use a toothbrush for better cleaning. 
  • After cleanup, let the filter dry and screw it back in place. Reassemble the heater front panel and check for codes now.

4. Blocked Neutralizer

If still, the error code is appearing on the screen, be sure the clogged neutralizer is the major reason here. All tankless water heaters including the Rheem model equips a neutralizer that is used to filter the acidic eater or condensate from the secondary heat exchanger. 

rheem tankless water heater blocked neutralizer

That’s how it plays great in preventing corrosion within the system through filtering. Due to contact with the hard water, there will form mineral on the pipe and create a block on the neutralizer. 

When the neutralizer pipe is blocked, there will be no longer a continuous flow of water, and the inside temperature of the unit fails to reach the set temperature. So in this step, you have to inspect the neutralizer for any blockages.

How To Fix:

First up, flip the circuit breaker of your water heater into the “Off” position Unscrew the front panel of the water heater. Now locate the neutralizer as we have shown in the above picture.

If you have a newly installed tankless system, chances are there is still a cap at the bottom for why the neutralizer is filled up. As a fix, remove the cap and inspect the drain for any clogs. 

Drain some water neutralizers using the service drain. The water should go through a single line with no loop and there should be no clog in the plastic drainage tube at the bottom left corner. 

rheem tankless water heater plastic drainage tube

Detach the valve from the tube to drain the water. If it’s clogging, clean the pipe and reconnect it to the tubing. 

If it is beyond cleaning, you need to replace it. Get this effective video to deal with the corroded neutralizer on your Rheem tankless water heater. 

5. Blockage In The Condensate Drainage System

In most cases, error code 29 appears on the display due to the blockage in the condensate drainage system. A condensing water heater uses the draining system to remove the condensate. 

blockage condensate drainage system

Now if the line is blocked by the crap builds, the condensate line gets clogged and back up which leads to error 29 eventually. The only solution is cleaning the condensate drain lines.  

How To Fix:

First off, locate the condensate drain port and line for your water heater.  It may combine with the AC or washing machine draining line and goes down to a P-trap at the floor level. This will be a 3-4 feet vertical pipe. See the picture above:

Take a vacuum suction to clean the condensate line. Also, you can remove the clog with a plumber’s snake. Flushing the drain port with white vinegar or any other cleaning solution is another effective method to clean the drain line. 

Allow the solution to soften the stuck debris for about 30 minutes.  Then again flush the drain with water. Never bleach or any harsh chemical to clean the drain line as it may damage the plastics and siding.

6. Incorrect Condensate Line Piping

Most of the time, incorrect installation of the condensate drain line creates obstruction in draining the proper condensation of the system. Then it causes the drainage backup and you will find the trouble code 29 on the display. 

There are a few factors for malfunction from the drainage pipe. Like 

  • Too much upward sloping of the drain line.
  • Incorrect size piping.
  • Or, trapped drain line.

How To Fix:

First off make sure that the drain cap on the bottom plastic tube is removed. Ensure the drain pipe is in the correct size and properly slopes down with a p-trap at the floor level. 

Avoid using a metal condensate pipe as it is corrosive and has a chance of deterioration quickly. Instead, it will be better to install a plastic fitting. 

We recommend contacting a professional to handle the condensate drain pipe installation for your tankless water heater. 

7. Defective PCB

If all the above troubleshooting has been ruled out, the defective PCB of your water heater is now the culprit to blame for trouble code 29.

All tankless water heater system equips a PCB or Printer Circuit Board that every process of the system switches, sensors, and thermostats. 

faulty PCB in rheem tankless water heater

Basically, it is the brain of the system. If anyhow, the PCB starts malfunctioning, it will fail to communicate with the entire system. 

Here you need to determine and replace the bad PCB.

How To Replace Faulty PCB In Rheem Tankless Water Heater?

Here are the simple steps to replace the PCB on the tankless system:

Step #1: Turn off the power connection to your water. If it’s gas power, don’t forget to turn off the gas shut-off valve and water supply.

Step #2: Now unscrew the front access panel and set it aside. Locate the PCB from the bottom of the inside assembly.

Step #3: Start by detaching small wires and connectors from the PCB connection. It will be better to take a picture or short note of the connection before disconnecting them so that you can put them right place while installing the new PCB. 

Step #4: Unscrew the two retaining screws from the bottom that connect the PCB with the leak detectors. Remove the mounting screws of the PCB.

Step #5: After removing all the wires and connectors, gently pull the PCB out of the chassis. 

Step #6: Install the new PCB back in place and complete the installation. If you’re technically inclined, watch the video that may help you to complete the task effectively. 


How do you clear a Rheem error code?

First, address all the responsive factors for that specific error code and resolve those. Then erase that hard lockout error code from your tankless water heater by pressing the power button.  

How long does a neutralizer last?

It depends on the maintenance of your water heater and how much acidic water is going through this element. But in general, a condensate neutralizer lasts approximately 3-5 years.

How to prevent rust on the water heater?

There are a few well effective methods to prevent rust on the tankless water heater. That includes inspecting the anode rod once a year for any damage, flushing the water heater at least 2-3 times per year, installing a water softening or filtration system near the water heater, and so on.

In Bottom!

Rheem water heater shows error code 29 mainly due to a malfunction of the heat exchanger. Here the heat exchanger temperature goes down mainly due to corrosion buildup or when the resistance to the thermistor goes out of range. 

So, you have to fix the heat exchanger issue first. If that doesn’t prove well, inspect the neutralizer to check whether it is filled up with condensate. If so, clean the drainage system. Head to a professional to handle the technical issues.

Well! That’s all from us here. Hope that you have no more queries left over on Rheem tankless water heater code 29. Don’t forget to share your valuable thoughts through comments.

” You can read our guide on Rheem tankless water heater code 11“.

About William

William is the founder of Fireplacehubs.com. 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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