Rheem tankless water heater error codes
12 codes that Rheem publishes for its tankless water heaters, each with what it means, the likely cause, what you can safely check and when to call a licensed professional. Tap your code:
If you smell gas
Stop: do not reset, relight or check anything on this page. Rheem’s own words, from the front cover of Use and Care Manual AP22009 Rev 04, under “What to Do If You Smell Gas”:
- Do not try to light any appliance.
- Do not touch any electrical switch; do not use any phone in your building.
- Immediately call your gas supplier from a neighbor’s phone. Follow the gas supplier’s instructions.
- If you cannot reach your gas supplier, call the fire department.
- Do not return to your home until authorized by the gas supplier or fire department.
Calling from a neighbor’s phone means leaving the building first. Source: High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone. Everything else is for a licensed professional — in the manuals’ words, a qualified installer, service agency or the gas supplier. If you smell gas, do none of the checks: follow the maker’s gas-smell instructions at the top of the page. Codes that need one are marked Licensed pro.
Read this first
Rheem tankless water heaters show their error code on the remote control. This page follows the Service Error Code Chart in the Use and Care Manual of Rheem’s high-efficiency non-condensing tankless heaters (AP22009 Rev 04, the RTG and RTGH series). Before the chart, Rheem gives one reset routine for every code: turn off the hot taps, turn the heater off at the remote, wait about 5 minutes, turn it back on and open a hot tap. If the code is still there, turn it off, unplug it for about 30 seconds, plug it back in, follow the chart and try again. If it still shows, note the code and call for service. Rheem’s manual also says: if the code is not in its chart, turn the heater off immediately and call for service.
11 Gas shut-off valve not fully open
- What it means
- The heater did not get enough gas to light — Rheem’s chart names the gas shut-off valve.
- Likely cause
- The gas shut-off valve on the outside of the heater is not fully opened.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Check the gas shut-off valve on the outside of the heater and open it completely (counterclockwise to ON).
- Then do Rheem’s reset routine at the top of this page.
- When to call a licensed professional
- If 11 stays with the valve fully open, call a dealer or qualified service technician.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
12 Gas supply interrupted, or propane running low
- What it means
- The burner’s gas supply stopped.
- Likely cause
- Gas service to the house has been interrupted, or, on a propane model, the tank is running low.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- If gas service has been interrupted, contact your gas utility company.
- On propane, refill or replace the LP gas container.
- When to call a licensed professional
- If gas is reaching the house and 12 stays, call a dealer or qualified service technician.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
90 99 Air intake or exhaust blocked
- What it means
- The heater cannot get combustion air in or exhaust out.
- Likely cause
- A blocked air intake or vent exhaust opening, or vent pipes not connected properly at the vent termination.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Remove any blockage at the air intake and exhaust openings. Rheem says the air intake needs 12 inches (30 cm) of clearance.
- When to call a licensed professional
- If the vent pipes at the termination may be disconnected, or the code stays, contact a dealer or qualified service technician.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
P1 Not enough water flow
- What it means
- Too little water is flowing through the heater for it to operate.
- Likely cause
- The hot tap is not open far enough to reach the heater’s minimum flow.
- What you can safely check
Tankless gas water heater: do only the owner checks its manual gives for that code — open the gas and water shut-off valves, check a propane tank has gas, clean a filter the way the manual shows you, clear snow or debris from the vent ends outside, turn it off and on at the controller. Leave gas pressure, the burner, the gas valve, wiring and circuit boards alone.
- Increase the water flow from the fixture: open the hot tap further.
- When to call a licensed professional
- If P1 shows with the hot tap fully open, call a dealer or qualified service technician.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
1L Lime (scale) build-up
- What it means
- The heater has a build-up of lime deposits.
- Likely cause
- Hard water leaving scale inside the heat exchanger.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Rheem’s solution is to contact a dealer or qualified service technician — a licensed professional.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
88 Flushing or filter reminder
- What it means
- A reminder to flush the heat exchanger and/or replace the water treatment filter. Rheem’s manual says this maintenance notice is optional and inactive by default, so you only see it if it was switched on.
- Likely cause
- The maintenance interval has run out.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Rheem’s solution is to contact a dealer or qualified service technician — a licensed professional.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
14 Water heater overheating
- What it means
- The heater is overheating.
- Likely cause
- Rheem’s chart gives no owner cause.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Rheem’s solution is to contact a dealer or qualified service technician — a licensed professional.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
31 33 Faulty thermistor (temperature sensor)
- What it means
- 31: faulty inlet thermistor (cold water in). 33: faulty outlet thermistor (hot water out).
- Likely cause
- A failed sensor.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Rheem’s solution is to contact a dealer or qualified service technician — a licensed professional.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
61 Faulty blower motor
- What it means
- The combustion blower (fan) motor is faulty.
- Likely cause
- A failed blower motor.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Rheem’s solution is to contact a dealer or qualified service technician — a licensed professional.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
66 Faulty bypass motor
- What it means
- The motor of the bypass valve, which mixes cold water into the hot, is faulty.
- Likely cause
- A failed bypass motor.
- What you can safely check
Nothing for the owner to check: this one is for a licensed professional.
- When to call a licensed professional
- Licensed pro Rheem’s solution is to contact a dealer or qualified service technician — a licensed professional.
Source: Rheem, High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual (AP22009 Rev 04), Service Error Code Chart, pages 76–77 Checked 2026-09-29.
A code that is not listed here
The chart in this manual lists 12 codes, all here. Rheem’s other tankless models have their own manuals: if yours is not an RTG or RTGH non-condensing model, check its chart. A Rheem gas tank heater has no code display at all — it blinks a status light (see the gas water heater status-light pages). Rheem’s manual warns never to attempt repair of electrical wiring, gas piping, the remote control, burners, vent connectors or other safety devices.
We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.
Related pages
Source
Every code on this page comes from this page, published by Rheem and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.