Noritz Error Code 29 — What It Means
Noritz error code 29 indicates exhaust overheat — the flue exhaust temperature sensor detected temperatures above the safe threshold during operation. Similar to other tankless water heater brands, Noritz monitors the outgoing flue gas temperature to protect the venting system and detect combustion abnormalities. Code 29 fires when exhaust temperatures exceed safe limits, which most commonly points to scale buildup in the heat exchanger, a blocked vent, or inadequate combustion air supply.
Common Causes
- Mineral scale in the heat exchanger — Scale reduces water-side heat absorption, pushing excess heat into the exhaust stream; this is the leading cause in hard-water areas.
- Blocked or restricted flue termination — A partially blocked exhaust cap traps hot gases and raises exhaust temperature.
- Low water flow rate — Insufficient flow means water passes through the heat exchanger slowly, absorbs maximum heat, and leaves less heat for extraction; exhaust exits hotter.
- Faulty exhaust thermistor — The sensor reports falsely high temperatures due to calibration drift or an intermittent fault.
Step-by-Step Fix
- Check the vent termination — Inspect the exhaust vent cap at the exterior wall or roof penetration. Remove any debris, ice, or bird nest material blocking the opening.
- Inspect the air intake — On direct-vent (concentric) models, the air intake is in the same cap assembly. Ensure the intake is clear — a blocked intake causes oxygen-lean combustion that generates more heat per unit of fuel.
- Descale the heat exchanger — Using the service valves on the Noritz unit, connect a descaling pump and circulate citric acid solution for 45–60 minutes. Flush with clean water before returning to service.
- Check water flow rate — Open a hot water fixture fully and verify strong, unrestricted flow. Check the cold water inlet filter screen inside the unit for debris.
- Test the exhaust thermistor — With power off, disconnect the exhaust sensor connector and measure resistance. Compare to Noritz’s specification for your model. Replace if out of range.
- Reset the unit — Hold the reset button for 3 seconds or cut power at the disconnect. Restore and run a hot water draw to verify code 29 is cleared.
Parts Often Needed
| Part | Notes |
|---|---|
| Exhaust thermistor | Noritz model-specific; confirm part number for NC, NRC, or NRCP series |
| Descaling pump kit | Citric acid or white vinegar solution |
| Vent terminal cap | Replace if corroded, cracked, or blocked by animal activity |
Need Replacement Parts?
Finding the right replacement parts for your equipment is critical to getting it running again. Check current prices on Amazon — prices and availability change frequently.
When to Call a Pro
If descaling and vent clearing don’t resolve code 29, a technician with a combustion analyzer can verify that the air/fuel mixture is correct. Incorrect gas pressure or a failing gas valve modulator can also produce hot exhaust — this requires licensed gas appliance service.