Rheem Water Heater Error Code 12: Causes and Easy Fixes
Learn what Rheem water heater error code 12 means, what causes it, and how to troubleshoot and fix the problem safely.
ERROR CODES
6/15/20263 min read
Nothing is more frustrating than stepping into the shower and discovering your hot water is gone. If your Rheem tankless water heater is displaying Error Code 12, the unit is warning you that it has detected a flame failure during operation.
The good news is that this issue is often caused by simple problems that homeowners can troubleshoot themselves.
What Does Rheem Error Code 12 Mean?
Error Code 12 indicates that the water heater's burner flame has gone out unexpectedly while the unit was running.
In simple terms, the heater started burning correctly but could not maintain the flame. As a safety measure, the system shuts down and displays the error code.
Common Causes of Rheem Error Code 12
Several issues can trigger this error.
1. Insufficient Gas Supply
A lack of gas is one of the most common causes.
Possible reasons include:
Gas valve partially closed
Low gas pressure
Empty propane tank
Gas line restrictions
Without enough fuel, the burner cannot stay lit.
2. Dirty Flame Rod
The flame rod detects whether the burner flame is present.
If dirt, soot, or corrosion builds up on the rod, it may incorrectly signal that the flame has disappeared.
The heater then shuts down for safety.
3. Venting Problems
Tankless water heaters require proper airflow.
Blocked vents caused by:
Bird nests
Leaves
Debris
Snow accumulation
can disrupt combustion and cause flame failure.
4. Faulty Gas Valve
A malfunctioning gas valve may not provide a steady flow of fuel to the burner.
When the fuel supply becomes inconsistent, the flame may extinguish unexpectedly.
5. Electrical Connection Issues
Loose wiring or damaged electrical components can interfere with flame detection.
The heater may mistakenly believe the flame is lost even when combustion is occurring.
6. Strong Winds
Outdoor installations are sometimes affected by high winds.
Strong gusts can blow out the burner flame or disrupt proper combustion.
How to Fix Rheem Error Code 12
Before beginning any repairs, always follow safety guidelines and turn off the unit if necessary.
Step 1: Reset the Water Heater
Many temporary glitches can be resolved with a reset.
Turn off the unit.
Wait 30 seconds.
Turn it back on.
Check if the error returns.
Step 2: Verify Gas Supply
Check the following:
Gas valve is fully open
Propane tank has fuel
Other gas appliances are functioning normally
If multiple appliances are affected, contact your gas provider.
Step 3: Inspect the Vent System
Look for any visible obstructions.
Remove:
Leaves
Dirt
Insect nests
Bird nests
Ensure air can move freely through intake and exhaust vents.
Step 4: Clean the Flame Rod
A dirty flame rod is a frequent culprit.
Turn off power and gas.
Locate the flame rod.
Remove it carefully.
Clean gently using fine sandpaper or steel wool.
Reinstall and test the unit.
Step 5: Check Electrical Connections
Inspect visible wiring for:
Loose connections
Corrosion
Damaged wires
If you are uncomfortable working with electrical components, contact a professional technician.
Step 6: Call a Qualified Technician
If the error persists after basic troubleshooting, professional diagnosis may be required.
The technician can test:
Gas pressure
Gas valve operation
Control board functionality
Flame sensor performance
How to Prevent Error Code 12
Regular maintenance helps prevent future flame failures.
Schedule Annual Maintenance
Have the unit professionally inspected once per year.
Routine service can identify small issues before they become expensive repairs.
Keep Vents Clear
Periodically inspect vent openings and remove any debris.
This is especially important during fall and winter months.
Clean Components Regularly
Keeping the burner and flame sensor clean improves reliability and efficiency.
Monitor Gas Supply
For propane systems, avoid letting tanks run completely empty.
Consistent fuel pressure helps maintain stable burner operation.
When to Seek Professional Help
Contact a licensed technician if:
Error Code 12 repeatedly returns
You smell gas
The burner fails to ignite
You suspect a gas pressure issue
Internal components appear damaged
Gas-related repairs should always be handled with caution.
Final Thoughts
Rheem Water Heater Error Code 12 usually indicates a flame failure caused by gas supply issues, dirty flame sensors, vent blockages, or faulty components. In many cases, a simple reset or cleaning of the flame rod can restore normal operation. However, recurring problems should be inspected by a qualified technician to ensure safe and reliable performance.
By performing regular maintenance and keeping vents and sensors clean, you can significantly reduce the chances of seeing Error Code 12 in the future.
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