BoilerFaultCodes E291 High
Boiler Fault Code E291
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code E291 appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has detected that the hot water flow and the cooler return water are being identified in the wrong order, likely due to a sensor misreading or a plumbing configuration issue. (As reported on Navien NCB)
Pick your boiler brand for the E291 fix
Source
Information for the E291 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026