Noritz Error Code 10: Combustion Abnormality Warning (Meaning, Causes, Fixes)

What the code means

Noritz's Knowledge Base article for its Pro Series models says error code 10 indicates a combustion abnormality and is usually a precursor to the more severe error code 90. Noritz says to treat 10 as a warning of more serious problems, and that the troubleshooting steps for 10 and 90 are the same. It lists three groups of causes: incorrect installation settings; low air flow, such as incorrect venting or dirty or clogged terminations or filters; and low gas flow or heating value, such as an undersized or too-long gas line or too small a gas meter. Any of these keeps the heater from producing the right hot water outlet temperature. On the EZ98DV, EZ111DV and NCC199CDV, the Noritz EZ service manual lists (F) 10 as a combustion abnormality that is only memorized in the error code history, so you may find it there rather than on the display. Its checkpoints are the air supply vent, the exhaust vent, a professional gas pressure check, a clogged or frozen condensate drain line, the slope of the condensate drain pipe, and the dip switch settings on the circuit board. If the display shows 908 instead, Noritz says an internal lock has been activated and the error can't be reset by you.

Likely causes

• A blocked or obstructed air supply (intake) vent, or dirty, clogged terminations or filters
• A blocked or obstructed exhaust vent
• Incorrect installation settings, such as elevation, vent type, vent length, vent size or common vent
• Low gas pressure or low gas heating value, for example a gas line that is too small or too long, or a gas meter that is too small
• On condensing EZ models, a condensate drain line that is clogged or frozen, or a drain pipe that doesn't slope down

Safe DIY checks

1. Treat 10 as a warning. Noritz says it usually comes before error code 90, which shuts the heater down, so deal with it now.
2. Look at the intake and exhaust terminations outside and clear anything blocking them, such as leaves, snow, lint, nests or debris. Indoors, make sure the air supply area isn't blocked by dust, trash or towels.
3. If the heater has an intake filter or screen, check that it isn't dirty or clogged.
4. On a condensing model, check that the condensate drain line isn't clogged or frozen and that it slopes down all the way.
5. Reset the heater by disconnecting the power and then reconnecting it, as Noritz instructs.
6. If 10 comes back after the vents are clear, stop there and call a service agent or Noritz at 866-766-7489. Gas pressure and setting changes are a job for a professional.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 11 Noritz Tankless Water Heater 11
• 12 Noritz Tankless Water Heater 12
• 14 Noritz Tankless Water Heater 14
• 20 Noritz Tankless Water Heater 20
• 29 Noritz Tankless Water Heater 29

All Noritz codes →

Sources

1. Noritz Knowledge Base, Error Code 10 (Pro Series Models): combustion abnormality, precursor to error code 90 with the same troubleshooting, causes (installation settings, low air flow, low gas flow or heating value), settings to verify, inlet gas pressure, power reset, 908 internal lock, technical assistance 866-766-7489
2. Noritz EZ98DV/EZ111DV/NCC199CDV Service Manual, Error Codes and Checkpoints p.31: (F) 10 combustion abnormality, only memorized in error code history, checkpoints (air supply vent, exhaust vent, gas supply pressure, condensate drain line and slope, dip switch settings) (HVAC Market copy)