Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
Noritz Error Code 12 — What It Means
Error code 12 on a Noritz tankless water heater indicates a flame failure — the unit attempted to ignite and the flame rod (ionization sensor) did not confirm a stable flame within the allowed time. Noritz units typically make two to three ignition attempts before locking out with code 12. This code covers both situations where the burner lit momentarily and lost flame, and situations where it never lit at all.
Common Causes
- No gas or low gas pressure — The most common cause. A closed gas shutoff valve, low line pressure, or insufficient BTU capacity on the supply line prevents the burner from establishing flame.
- Dirty flame rod — The ionization rod (flame sensor) accumulates silicon oxide deposits from combustion byproducts. A coated rod cannot pass the microamp signal needed to confirm flame to the control board.
- Failed igniter — A cracked or failed spark igniter won’t produce the spark arc needed to light the gas-air mixture.
- Blocked air intake or exhaust — A restricted combustion air supply or blocked exhaust prevents proper combustion, causing the flame to go out immediately after ignition.
Step-by-Step Fix
- Confirm gas supply — Open all gas shutoff valves and confirm other gas appliances are working normally. If the gas meter has a seismic shutoff (common in California and Japan-influenced markets), check and reset it.
- Clean the flame rod — With power and gas off, remove the flame rod from the burner assembly (typically one screw and a push-on connector). Clean the rod tip with fine steel wool or 400-grit emery cloth. Reinsert and reconnect.
- Inspect the igniter — With power off, visually inspect the spark igniter tip for cracking or carbon buildup. A cracked porcelain igniter should be replaced. Clean light carbon deposits with a dry brush.
- Check combustion air intake — Inspect the combustion air intake screen (on the bottom or side of the unit) for blockage. Clear any lint, debris, or insect nests.
- Clear code 12 and test — Press and hold the ON/OFF button for 3 seconds to reset, or power-cycle the unit at the breaker. Initiate a hot water draw and listen for spark and burner ignition.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame rod / ionization sensor | Clean first; replace if corroded or wire insulation is damaged |
| Igniter assembly | Match Noritz model (NRC, NRCR, EZ series vary) |
| Gas valve | Replace if voltage present at coil but valve won’t open |
| Air intake screen | Clean or replace if blocked |
Need Replacement Parts?
Before ordering, match the water-heating part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Gas pressure testing and gas valve replacement require a licensed plumber or gas technician. If code 12 persists after cleaning the flame rod and igniter, have a Noritz-certified technician verify gas manifold pressure and gas valve operation.