BoilerFaultCodes 6.4.2 Thermostats High
Boiler Fault Code 6.4.2 Thermostats
Also written as 642THERMOSTATS — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 6.4.2 Thermostats 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 a safety thermostat has tripped, causing it to shut down to prevent the system from overheating. (As reported on Remeha Quinta 30)
Pick your boiler brand for the 6.4.2 Thermostats fix
Source
Information for the 6.4.2 Thermostats 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