Rheem Tankless Gas Code P1
No hot water delivered. A warning code about hot water not being delivered when there is a demand for it. Rheem's own first response is a specific power-and-water cycle: turn the water supply to the unit off, turn the remote control off, wait ten seconds, turn the remote back on, then turn the water supply back on.
DIY fixThe verdict
No parts needed — reset or re-check a setting
Start with Rheem's own reset sequence — it costs nothing and it clears the transient version of this. If the warning returns, the next questions are about water flow reaching the unit at all, which is where the inlet filter and the isolation valves come in.
Typical cost: $0–$500
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. 31), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Turn the water supply to the unit off.
- Turn the remote control off, wait ten seconds, and turn it back on.
- Turn the water supply back on and run a hot tap.
- If it returns, check the isolation valves are fully open and clean the inlet water filter before calling anyone.
Frequently asked questions
Why does the reset involve the water supply and not just the power?
Because the unit needs to see flow stop and start to re-establish where it is in its own sequence. Cycling the remote alone does not do that.