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Water Heater / Boiler Error Codes: All Brands

Gas boiler fault codes usually indicate an ignition failure or lockout, low system pressure, overheating, or a problem with the fan or flue. The safe user checks are limited: read the pressure gauge (many residential systems run around 12–15 psi when cold), confirm that other gas appliances work, and try the reset button once. If the code returns, or you smell gas or a carbon monoxide alarm sounds, stop there and call a licensed heating technician or your gas utility – these pages contain no repair instructions for gas appliances.

12Codes
3.0Average severity
17%High or critical
0%DIY-friendly
Severity distributionSeverity distribution

ENERGY STAR certified models

Viessmann · Water Heater / Boiler22
Bosch · Water Heater / Boiler16
Buderus · Water Heater / Boiler4

Source: ENERGY STAR open data (data.energystar.gov) – number of certified models currently listed.

Official safety recalls (US CPSC)

Source: US Consumer Product Safety Commission recalls API. Check your model and serial number on the linked recall notice.

All codes (12)

10 Rinnai · Water Heater / Boiler The Rinnai can't breathe: a frozen condensate line, a blocked vent terminal or a dirty air… High 11 Rheem · Water Heater / Boiler Rheem tankless didn't light at startup. Rheem's own first fix: check the gas shut-off valve… Moderate 11 Rinnai · Water Heater / Boiler The Rinnai tried to light but never proved a flame – gas off, air in the line or low gas… Moderate 12 Rinnai · Water Heater / Boiler The Rinnai lit but then lost its flame or stopped sensing it – usually gas supply, venting… Moderate 29 Rheem · Water Heater / Boiler Condensing Rheem tankless: acidic condensate can't drain, so the heater stops before it floods… Moderate E003 Navien · Water Heater / Boiler The heater sparked and opened its gas valve, but never saw a flame – often a closed valve or no… Moderate E012 Navien · Water Heater / Boiler The burner lit, then lost its flame signal mid-cycle – think gas pressure, grounding or a dirty… Moderate E02 A. O. Smith · Water Heater / Boiler The tank water got hotter than the safety limit, so the ECO cut power to both elements – reset… Moderate E04 A. O. Smith · Water Heater / Boiler The electronic thermostat can't power the upper element; the lower one still works, so hot… Low E110 Navien · Water Heater / Boiler The fan can't move enough air through the vent system – most often a clogged intake filter… High E351 Navien · Water Heater / Boiler Navien combi boilers: the auto make-up water valve couldn't restore heating pressure within 5… Moderate LC Rinnai · Water Heater / Boiler Mineral scale is coating the heat exchanger – the Rinnai needs a descaling flush; the digit… Low

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