BoilerFaultCodesRemeha code9 Fault Code
Also written as CODE9 — same fault.
The Remeha code9 fault code means: your boiler has switched itself off because an external safety device, such as a thermostat or pressure switch, has detected an issue and broken the electrical circuit.. It appears on 1 Remeha model in our database.
Technical description: External interlock circuit is open (e.g., external gas pressure switch or safety thermostat for under floor heating activated); the boiler will shut down.
What causes the Remeha code9 fault?
This fault occurs when an external safety component connected to the boiler’s control board detects a potential hazard and breaks the electrical circuit to stop operation. The most common reason is an underfloor heating safety thermostat triggering because the water is too hot, or a gas pressure switch detecting that the incoming fuel supply is unstable.
This issue is more common in winter when high demand on the local gas network can cause pressure fluctuations that trigger external safety switches.
DIY fix possible
Check if your room thermostat or programmer is set too low or has run out of batteriesIf you have underfloor heating, check if the floor has overheated and tripped the safety limitReset the boiler by pressing the reset button for two seconds
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Gas Safe Register →Remeha models that show the code9 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Remeha code9 fault code information on this page is sourced and cross-checked against the official Remeha service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026