Boiler Fault Code 6.4.7 Down draft thermostat

Also written as 647DOWNDRAFTTHERMOSTAT — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 6.4.7 Down draft thermostat appears across 1 boiler brand and 2 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 exhaust gases are being blown back into the unit instead of venting safely outside, so it has shut itself down to prevent a fire or carbon monoxide risk. (As reported on Remeha Quinta 30)