Which models this covers
Rheem RTGH condensing and RTG non-condensing gas tankless water heaters (Use & Care AP21820 and AP22009), plus the “-3” generation in Rheem’s Troubleshooting Manual AP21822 (including RUTGH/RMTGH, ECOH and RUTG/RMTG/ECO models). Older “-2” units may differ. Codes differ between control boards, so check the code chart printed on your unit or in its manual if your model isn’t listed.
How to read the code
The code shows on the unit’s display or remote. Rheem’s general reset: turn off all hot water taps, switch power off and on, and wait 5 minutes. If the code stays, unplug for 30 seconds. If it’s still there, call for service.
Error codes
| Code | What it means | What to do |
|---|---|---|
| 10 | Incorrect inlet air volume (venting or blower) | Call a pro.Pro |
| 11 | Gas shut-off valve not fully open | Check the gas shut-off valve to the heater and open it fully. |
| 12 | Gas service interrupted, or propane running low | Contact your gas utility, or refill the propane tank. |
| 14 | Overheating | Call a pro.Pro |
| 16 | Outlet water temperature above set point / outlet sensor | Call a pro.Pro |
| 1L | Lime (scale) build-up in the heat exchanger | Contact a dealer or qualified service technician to flush the unit.Pro |
| 29 | Condensate neutralizer clogged / drain trap not draining (condensing models) | Call a pro.Pro |
| 88 | Flush / filter maintenance reminder | Schedule service to flush the unit and clean the filter.Pro |
| 90 / 99 | Air intake or vent blocked | Clear any blockage (snow, leaves, nests) and keep 12 inches of clearance. If it returns, call a pro.Pro |
| P1 | Not enough water flow | Open the hot water fixture further. Check for clogged aerators or a dirty inlet filter. |
Sources
These codes are transcribed from the manufacturer’s own documentation. Many websites repeat codes that don’t match the manuals, so when in doubt, trust the chart on your unit.
- Rheem RTGH Use & Care Manual AP21820
- Rheem RTG Use & Care Manual AP22009
- Rheem Tankless Troubleshooting Manual AP21822
Code pointing to a big repair? Check whether to repair or replace before you pay for it.
Frequently asked questions
What does code 11 mean on a Rheem tankless?
On Rheem tankless heaters, 11 means the gas shut-off valve isn’t fully open. Check the gas valve on the line to the heater and open it fully, then reset the unit.
Is there an LC code on Rheem tankless water heaters?
Current Rheem tankless manuals don’t use LC. Rheem shows lime build-up as 1L, and 88 as a flush/filter reminder. LC is a Rinnai code, which is why some websites mix them up.
How do I reset a Rheem tankless water heater?
Turn off all hot water taps, switch the power off and back on, and wait 5 minutes. If the code is still there, unplug the unit for 30 seconds. If it persists, call for service.