Rheem code 03: communication failure

Larger homes and commercial systems sometimes link several tankless heaters so they work as one. Code 03 means the units, or their controls, have stopped talking to each other.

This page uses two Rheem sources: the current Rheem and Ruud tankless troubleshooting manual, and Rheem's error code list for earlier tankless models. Codes can differ between generations, so the meaning for each is shown where they differ. Rheem technical support: (800) 432-8373.

What it means by model generation

What a technician checks

• The communication cables between units and the manifold controller, for loose, damaged or reversed connections
• The DIP1 switch settings on each control board, which tell each unit its role in the system
• The remote control wiring
• Whether a control board has failed

What you can do

1. Note whether work was done near the units or their wiring recently.
2. Turn the system off and on once.
3. If code 03 returns, call a technician familiar with multi-unit systems.

How to reset it

1. Close all hot water taps.
2. Turn the remote control off, wait about 10 seconds, then turn it back on.
3. Open a hot tap and watch whether the code returns.

Before you call

Have the model and serial number from the rating label ready, and note whether your unit is a condensing (high-efficiency) or non-condensing model. Tell the technician the exact code, when it appears and any recent work on the gas, water, venting or electrical supply. That often saves a second visit.

See every code on our Rheem error codes page.