Rheem Tankless Gas Code 03
Communication failure between units or controls. Only appears on manifold installations — several water heaters linked through an EZ-Link, MIC-6 or MIC-185 controller. It reports a communication failure between the water heaters, the remote control, and/or the manifold controller. Rheem's checks are the DIP1 setting on each control board and the Molex connectors on all boards.
Call a proThe verdict
Call a licensed plumber
Not a component failure and not something a single-unit installation should ever show. On a manifold system it is usually a switch setting or a connector, which makes it one of the cheaper faults — but it is inside the cabinets of gas appliances.
Typical cost: $0–$400
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Tankless Gas — not averaged across the brand.
Source: Rheem Tankless Gas Troubleshooting Pocket Manual (SVC820) (p. 34), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Note how many water heaters are in the system and whether they all show the code.
- If anything was recently added, replaced, or rewired in the manifold, contact that installer.
- Do not open the units to change switch settings yourself.
Frequently asked questions
I have one water heater and I am seeing 03.
Then something is configured as though it were part of a manifold. Rheem's own note is that this code is only for manifold installations, so say that when you call — it changes where the technician looks.