Rheem Tankless Water Heater Error Code 12: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Rheem tankless water heater error code 12 means: Gas service has been interrupted, or on LP models the propane supply is running low. [1] Keep using it? No hot water until it's resolved. Don't keep resetting it.. Start with the owner checks below, beginning with: check other gas appliances.

Smell gas? Leave the building now. Do not touch light switches, phones or appliances inside. Call your gas utility or 911 from outside. CO alarm sounding or headache, dizziness or nausea? Get everyone outside and call 911. Gas valves, burners, venting and wiring are for a licensed technician only. See our safety policy.

Quick facts

Code	12
Also shown as	None listed by the manufacturer
Brand / appliance	Rheem tankless water heater (rtgh high-efficiency non-condensing tankless gas water heaters (use and care manual))
System	Heating
Official meaning	Gas service has been interrupted, or on LP models the propane supply is running low. [1]
Keep using it?	No hot water until it's resolved. Don't keep resetting it.
DIY-safe?	Owner checks only (listed below)
Support	Rheem tankless support, 1-866-720-2076

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code 12 means on a Rheem tankless water heater

Gas service has been interrupted, or on LP models the propane supply is running low. [1]

This is a heating code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Rheem tankless water heater error code 12 (safe owner checks)

Owner checks only: on heating, cooling and water-heating equipment, limit yourself to reading the code and checking the thermostat, breaker and service switch, air filter, condensate drain, that the gas supply valve is open (no disassembly) and that vent terminals are clear of snow or debris. Reset power only if your manual allows it.

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on Rheem's published guidance [1], rewritten for clarity.

Check other gas appliances. If other gas appliances also don't work, contact your gas utility company.
LP models: check the tank. Refill or replace the LP gas container.
Restart the heater. Turn off the hot water faucet, turn the heater off with the POWER ON/OFF button, wait about 5 minutes, then turn it back on and recheck the remote display.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

No specific part is implied by the manufacturer's guidance for this code.

When to call a technician

Gas pressure, gas valve, igniter, flame rod, venting or combustion problems: licensed plumber or gas technician
Gas valves, burners, igniters, flame sensors, venting/flue or CO concerns: licensed HVAC technician or plumber
Refrigerant work: EPA 608-certified technician only
Smell of gas: leave and call the gas utility or 911
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Rheem tankless support, 1-866-720-2076 first

Frequently asked questions

What does error code 12 mean on a Rheem tankless water heater?

Rheem lists 12 as follows: Gas service has been interrupted, or on LP models the propane supply is running low.

Is it safe to keep using the tankless water heater with 12?

No hot water until it's resolved. Don't keep resetting it..

Can I fix Rheem tankless water heater error 12 myself?

Only with the owner checks on this page, starting with: check other gas appliances. If it persists, call a technician or Rheem tankless support, 1-866-720-2076.

Sources

https://files.rheem.com/blobazrheem/wp-content/uploads/sites/2/RTG-Use-and-Care.pdf (official)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Rheem.