Rheem tankless water heater code 99 is the error indication that the fan motor isn’t creating enough ventilation. The ventilation system has successfully passed the pre-purge but has failed during normal operation.
If your Rheem displays error code 99, here are the possible reasons to check for:
- Blocked or obstructed heat exchanger fins
- Clogged air intake filter
- Malfunctioning blower motor
- Or blockages in the venting lines
As an obvious solution, reset the hard lockout due to appearing the error code 99. If the error persists, inspect the exhaust vents, heat exchanger, air intake filter, or blower motor for any blockages. Clean out the elements correctly and ensure all are working well.
Hold on tight with us to learn the effective procedures to erase the error code in no time.
Table of Contents
Possible Reasons & Solutions To Rheem Tankless Water Heater Code 99 [Quick Overview]
Before jumping to the details, let’s have a short glimpse of all the probable reasons and solutions for Rheem tankless water heater error code 99.
| Probable Reasons | Possible Solutions |
| Hard lockout | Reset the hard lockout through the Dip Switches on the PCB. |
| Blocked exhaust and venting flue | #Clean out the venting lines properly. #Ensure the venting is sealed according to the manufacturer’s instructions. #Also, Visually inspect venting for the use of correct venting material, termination, and lengths. |
| Clogged heat exchanger | Remove all the accumulated dust and debris from the heat exchanger fins. |
| Clogged air inlet filter | Inspect the air filter for any possible blockage and clean it. |
| Malfunctioning blower motor | Clean the blower motor first and ensure it gets the right PCB voltage. |
How To Fix Error Code 99 On Rheem Tankless Water Heater [Easy Solutions]
Well, after previewing the quick solutions, let’s move ahead to the detailed troubleshooting to deal with the error code 99 on your Rheem tankless water heater.
Let’s start with learning how you will reset the code through the dip switches on the PCB. Here you go!
1. Reset The Hard Lockouts For Rheem Error Code 99
If your Rheem controller displays the error code 99, be sure it has put your water heater into a Hard Lockout condition, in which the unit won’t operate. As a solution, you will have to reset this lockout. After that, the best possibility is that the error code will be erased.
If you are wondering about Rheem error code 99 reset, here is all you’ll have to follow out:
How To Reset Error Code 99 On Rheem Tankless Water Heater?
Follow the step-by-step procedures below to reset the hard lockout for Rheem tankless water heater error code 99:
Step #1: Start by turning off your water heater. In this instance, turn off the remote control first and unplug the unit from the power connection.
Step #2: Now remove the front cover panel of your water heater to inspect the control board inside. Then locate the Dip switches on the control board.
Step #3: First, ensure that all the dip switches are in the Off position, meaning all will be in the Down Side.
Step #4: Locate the Dip Switch 2 and turn it to the On position. Then immediately turn it off. Use a sharp object if needed.
Step #5: Within 5 seconds, press and hold the MIN and MAX button simultaneously. Keep pressing the buttons for about 2 seconds.
Step #6: The remote control will start flashing “UL,” then it will go solid, indicating that the heater has been reset. If so, release the buttons and turn on the remote control. You may operate your unit again.
If you’re struggling with any faulty history on your Rheem display, you can easily erase it by following the instructions in the Rheem Manual.
To perform it quickly, you can check our comprehensive guide on clearing Rheem’s fault history, highlighting all the required procedures.
2. Blocked Exhaust & Venting Flue
After resetting the hard lockout and still having the same error code 99 on the Rheem display, the exhaust & venting flue is the first suspect to blame. That’s the same case I also encountered with my water heater. To confirm this fact, I removed the vent structure from the unit and started operating my water heater again. The results just shocked me.
I found the error code disappeared, meaning the problem lies within the venting.
In case of your water heater, you may find that the venting lines of the unit are accumulated with dirt and debris, creating a combustion issue in the system.
Here are some common sources of water heater exhaust vent blockage:
- Rodents/birds inside the vent
- Soot buildup in the vent
- Snow blocking vent
- Damaged vent
- Corrosion/rusted-out vent
A blocked venting of a water heater can be a serious problem as it would cause carbon monoxide to build up in the system, affecting the overall functions of the heater. Even the poisonous carbon monoxide gas can push back into your house as well. At times, the system may shut off immediately as a safety precaution.
Thus a quick cleaning is quite needed. Here is all you need to know about how to clean water heater vents:
How To Fix:
Start by turning off the power supply to your water heater. Unplug your water heater from the power connection and simply flip the circuit breaker to the Off position. Now start cleaning as follows:
First off, inspect the exhaust for leaves or snow build-up, as they are the common sources for the heater vent blockage. If so, shovel away the snow so the vent can breathe or clear out the pile of leaves blocking your vent.
Well! When your vent is cleared from the external blockages, take a look at the vent inside.
There may be soot or debris build-up. Clean them out.
- Use a vacuum cleaner with a hose attached to clear out the inside of the vent.
- Or, use a brush and a soft cloth to remove dust as much as possible.
- Take a wire hanger and poke inside the vent pipe to clean the part that is hard to reach.
Note: Please wear a dust mask and rubber gloves to avoid filth and dust coming near you.
As with cleaning, you need to ensure the proper installation of your water heater. In this instance, speak with a professional to determine if the venting lines are correctly installed.
3. Clogged Heat Exchanger
Blockages in the heat exchanger fins are another major culprit to blame for the Rheem tankless error code 99 on the remote display. The heat exchanger is a set of metal shells and tubes that mainly works by transferring heat from one place to another.
When the heater burns the fuel, its exhaust/combustion by-products pass through the heat exchanger and provide hot water by heating the metal.
The blocked heat exchanger fails to pass through the exhaust, leading to abnormal combustion and triggering the error code 99.
How To Fix:
By following the steps above, you can effectively clean your heater’s heat exchanger effectively:
Turn off the power of your tankless water heater by flipping the circuit breaker to the Off position. Also, turn on the water and gas supply by using the shut-off valves.
Remove the front access panel and get access to the heat exchanger. Take a wire brush and remove any dirt or debris from the heat exchanger.
- Use a bristle brush to loosen any of the black soot or scale buildup in the tubes and coils.
- Take a strong vacuum cleaner with a higher suction power and vacuum the entire block assembly. Or, you can use a soft cloth dampened with a cleaner specifically to remove any remaining debris.
- Once you’re satisfied with the cleaning, now check the heat exchanger flapper valve at the vent connection to see whether it’s running freely. If needed, replace it.
- Reassemble the heat exchanger back in position and set up the front access panel. Restore the power supply and turn on the gas and water supply.
4. Filthy Air Intake Filter
The air inlet filter is another major component of a tankless water heater that is designed to keep bugs and dirt out of your system. In case it gets blocked by debris and shoots, the airflow will slow, and you will encounter abnormal combustion issues in your system.
In such cases, the exhaust gases fail to pass through the unit, affecting the blower motor functions. As a result, it is obvious the Rheem tankless water heater triggers the error code 99 on the remote display.
Don’t get in trouble! A quick cleaning of your air inlet filter is enough to resolve the issue.
How To Fix:
To clean the air intake filter, you will have to get access to this element first. But before that, make sure you’ve unplugged your tankless water heater from the power connection. Shut off the gas and water supply as well.
Now remove the front access panel and locate the air filter from the top right corner of the heater inside.
Remove the screw attached to the filter and slide it out from the connection. Now take a brush and remove the stuck debris from the filter screen.
If needed, take it under running water and wash off all the filters from the screen. When done, dry it off using a towel. Then reassemble the filter back in connection. After cleaning, restore the power supply to your heater and check for error code 99 on display.
If still, it’s appearing, don’t get in trouble. We have one more element as a suspecting factor for this issue. Let’s move on.
5. Blockages In The Combustion Fan
Last but not least, a malfunctioning blower fan is the major responsive factor to trigger the error code 99 on the Rheem tankless water heater remote display.
The best chances are the blower motor isn’t running freely due to accumulated dirt and debris. Another possibility is the blower motor isn’t getting the right voltage from the PCB, which is creating restrictions on the free moving of it.
Whatever the fact is, let’s inspect the blower motor to find out the actual faults.
How To Fix:
First up, inspect the blower motor for any clogs. To do so, you’ll need to dismount the blower motor by removing the screws holding it in its place. Slide it out from the connection, and be careful of the wires that are still attached to the housing.
Now the time comes for cleaning. Use a hose-attached vacuum cleaner for cleaning purposes. Vacuum out the debris between the fan motor and housing using the vacuum clear.
You can use a brush to remove the large clumps of dust efficiently. When done, try to turn the blower motor manually to see if it’s running freely.
After cleaning, look for damaged or loose wiring connections to the motor and fix those. Replace the worn-out wiring. You may need to test the blower motor electrically as well.
For this, here is a complete guide to check the resistance of your Rheem tankless water heater blower motor. You may need to replace the faulty blower motor or Printed circuit board.
After servicing the blower motor, I hope you are free from error code 99 on the Rheem tankless water heater display.
Frequently Asked Questions (FAQs)
What does it mean if there is no error code on the Rheem tankless water heater remote display?
There would be several meanings behind this. Check the power to ensure that the unit is actually plugged in. Check for tripped or turned-off circuit breakers as well. Also, there would be an incorrect flow rate or blocked water filter.
What does Rheem tankless water heater error code 76 mean?
Rheem error code 76 indicates a fault in the remote control communication. Check the wiring on the remote control for any loose or damaged connections. Disconnect the remote control and test the unit without the remote control.
Why is my Rheem tankless water heater not getting hot enough?
If there is no hot water from your Rheem water heater, higher chances are you have set the temperature too low. Or there would be frozen water piping, a wrong adjustment of the anti-scald valve, or a system overload issue.
In Closing!
Rheem tankless water heater code 99 is a clear indication of the blocked flue fault that is causing the blower motor to be unable to vent. At a minimum check, you’ll need to inspect the combustion fan, heat exchange, blower motor, and air intake filter for any possible blockages. There may also be blockages in the exhaust vents which should be removed.
Anyway, to prevent such errors in the future, you’ll need to be careful about the proper maintenance of your water heater. Inspect your tankless water heater at least once or twice a year and service it properly.
By doing so, you can ensure your tankless water heater is running efficiently. To get details on how you will maintain your Rheem tankless water heater, take a look at our comprehensive guide, highlighting all the instructions that you should know.