Rheem tankless water heaters display faults as short numeric codes on the unit or its remote controller. Code 11 means the burner failed to ignite, Code 12 means a flame that lit successfully was then lost during operation, and Code 76 points to a communication fault between the control board and the remote — three genuinely distinct problems that need different checks.
The checks below are limited to confirming gas supply and clear venting. Anything involving the burner assembly, gas valve, or flame rod itself should be handled by a qualified technician.
Code 11 — ignition failure
The unit tried to light the burner and failed. Common causes include the gas supply not fully on, a nearly empty propane tank, or blocked intake/exhaust venting restricting the combustion air the burner needs.
Code 12 — flame loss during operation
The unit lit successfully, then the flame went out mid-cycle, triggering a safety shutdown. This often comes down to marginal gas pressure that cannot keep up under full hot-water demand, a dirty flame rod, damaged flame rod wiring, or exhaust recirculation disturbing the burner.
Code 76 — communication error
This is a communication fault between the control board and the remote controller, most often traced to a loose, pinched, or corroded wire in the cable connecting the two.
How to check each one
- For Code 11, confirm gas supply first
Check the gas is on at both the unit’s shutoff valve and the main meter, and confirm a propane tank is not empty.
- Check intake and exhaust vents
Confirm both are clear of obstructions, snow, or debris — restricted venting affects both ignition and flame stability.
- Power-cycle the unit
Cut power for about 30 seconds, then restore it and try again.
- For Code 76, inspect the remote cable
Check the wire between the unit and the remote controller for visible damage, looseness at either connector, or corrosion.
When to call a professional
Code 11 and Code 12 both involve gas safety and internal combustion components — have a licensed technician inspect the burner, gas pressure and flame rod if the basic checks above do not resolve them. Code 76 is safer to investigate yourself since it is a low-voltage communication issue, but a technician can also replace the cable if needed.
Stop and call a qualified appliance technician or electrician if you find scorched or melted wiring, smell burning, see water that has reached electrical components, or if the fault returns immediately after a repair. Never bypass a safety device — thermal fuses, door interlocks and flood switches fail for a reason, and defeating one converts a broken appliance into a fire or flood risk.
