Rheem Tankless Water Heater Code P1: What It Means + How to Fix It

Not again! These vague codes are really getting frustrating. What in Pete’s name does P1 refer to again? Now you have to search through the maintenance manual for an answer—and the phonebook for a licensed plumber.

But hold on! Before you dial up that licensed plumber to answer questions about and fix your heater, there’s a chance you might actually solve this yourself.

Rheem’s tankless hot water heater error code P1 signals an issue with a low flow of water through your heater system, usually due to debris of some kind.

This article will cover the reasons why that pesky error code keeps showing up when you try to heat water and how to get rid of it. Generally, without forking out big bucks for a service technician.

Raheem water heater

What Is Rheem Tankless Water Heater Error Code P1?

Error code P1 is a common error code that indicates a low water flow in the water heater system. Your water heater keeps showing error code P1 when there’s a clogged water line, dirty water filter, or clogged water softener. 

Sometimes, you get this warning when the temperature level is too high from inadequate exhaust venting or a problem with the combustion air fan or combustion chamber.

Why Do I Keep Getting Error Code P1 in my Rheem Water Heater?

Low water levels are the reason why you keep getting error code P1. However, low water flows are just the tip of the iceberg; different underlying issues cause low water flow in water heaters. Let’s explore the root causes of low water levels in Rheem’s tankless units. 

Broken Dip Tube Reducing Water Flow to Unit

The dip tube transfers cold water to the bottom of a water heater. Water will remain at the top of the heater if the dip tube water leaks. Furthermore, a broken tube will significantly reduce water flow.

Sediment Buildup at Bottom of Water Heater

bottom of water heater

Calcium deposits and other minerals in water accumulate at the bottom of water heaters. The gradual buildup of these sediments can reduce water flow rate and the efficiency of water heaters. So, flush away the deposits at least once a year. Use vinegar to remove all stains effectively. 

Faulty Heating System

Check the thermostat or any other temperature-regulating component in the water heater system, such as the outlet water temperature sensor or water inlet temperature sensor. Contact a Rheem-licensed repairer to check and get a replacement if necessary. 

Tank is Too Small

Small-sized hot water heater tanks will run out of water quickly, especially when installed in a large household. Therefore, installing a large water tank may remove the error code P1. 

What Happens If I Ignore Error Code P1?

We don’t recommend ignoring this error code. A too-low water level can lead to overheating and melting pipes. It may also damage other heat-sensitive components. So, maintain the water level to avoid paying hundreds of dollars for another unit. 

How to Fix Error Code P1 in Rheem Tankless Water Heater 

fixing an error code p1 in rheem tankless water heater 

Fixing an error code P1 is quite a straightforward process. Ensure you have the necessary tools for working on the unit. For example, use the correct wrench size.

Clean the Aerator 

Aerators increase the steady flow of water from heaters. However, a clogged aerator will reduce water flow below the minimum flow rate. So, clean the aerator by removing it from the faucet and dipping it in vinegar. Rinse it under water for a few minutes.

Clean the Cold Water Inlet Pipe or Filter

Foreign materials can clog up the water inlet filter or pipe, giving an error code. To clean the inlet water supply filter:

  1. Drain the heater.
  2. Remember to turn off the heater.
  3. Open the drain valve.
  4. Open the faucet closest to the heater.

This will allow the air intake pipes to bring water flow into the tank. Note: Open the cold water supply valve a few times to stir the water and drain the unit altogether. Ensure the tank is empty. 

How to Reset Rheem Tankless Water Heater 

Reset the unit to delete the code via these steps:

  1. Switch on the heater circuit breaker. 
  2. Next, pry open the panel cover and locate the reset button.
  3. Push the button until it clicks into place and opens. 
  4. Furthermore, reconnect the gas valve. 
  5. The heaters should power on. Moreover, the reset button will cancel all error codes. 

What Should I Do If Resetting Does Not Remove the Error Code P1? 

You may need to press the reset button more than once to resolve the error code. In most cases, a single reset is often enough to solve the problem. Call a qualified service technician with service experience if the issue in your tankless unit persists.

Remember to take precautions when working with water heaters; a wrong step can cause water to enter the electric components. An alternative option is to contact Rheem customer service for assistance. Sometimes, the company may send a plumbing expert to assist and resolve the error code. So, check if your unit is still under warranty. You may be eligible for free replacements or labor.