BoilerFaultCodesRemeha 1-2-3 Fault Code
Also written as 123 — same fault.
The Remeha 1-2-3 fault code means: your boiler has detected a general issue that needs checking to prevent a full breakdown.. It appears on 1 Remeha model in our database.
Technical description: General warning signal
What causes the Remeha 1-2-3 fault?
This fault occurs when the boiler's internal computer detects an inconsistency in the electrical signals required to keep the system running safely. The most common reason is that the components responsible for lighting the flame or monitoring its presence are beginning to wear out or are sending weak feedback to the main control board.
DIY fix possible
Check that your home's gas supply is activeEnsure the system water pressure is between 1.0 and 2.0 barRestart the boiler by holding the reset button for two seconds
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Gas Safe Register →Remeha models that show the 1-2-3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Remeha 1-2-3 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