Rheem P1 Error Code: Not enough water flow
Updated October 2026 · Sourced from Rheem documentation
🧭 Check a few things first
The manual says there is not enough water flow to operate the unit.
Is it safe to keep running? Check the steps below first. If flow is normal at the faucets and the code keeps coming back, call a qualified service technician.
P1 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| P1 Shown on the LED display of the remote control | Not enough water flow | Rheem non-condensing tankless gas water heaters (160,000, 180,000 and 199,900 Btu/h models) with remote control display |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Open the hot water faucet further, or open a second hot fixture, to raise the flow, as the manual says.
- Check that the water supply valves to the heater are fully open.
- Check the faucet aerators for blockage if flow is low at only one fixture.
🛑 Stop and call a licensed pro if
- If flow is normal at the faucets and the code keeps coming back, call a qualified service technician.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Codes for flame failure, overheating, venting or the control board that return after one reset.
- Water leaking from the heater, the relief valve discharging, or scorching around the burner area.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Rheem code
- Write down the exact code shown on the controller or the number of status light flashes.
- Turn the water heater power off and back on (or press the reset button the manual describes) once. If the code comes back, stop resetting.
- Make sure the gas supply valve to the heater is open and other gas appliances in the home are working.
- Make sure the cold water supply valve is fully open and hot water taps are not partly closed.
- Look at the outside vent terminal for snow, ice, leaves or anything blocking it (look only).
Source: Rheem High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual, Service Error Code Chart, p. 77. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Ryan Giles · Red Seal Certified Plumber · Ask a plumber · Ask an HVAC technician
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