BoilerFaultCodesRemeha 1 8. Fault Code
Also written as 18 — same fault.
The Remeha 1 8. fault code means: your boiler has shut down because the water inside has become too hot, usually due to a lack of circulation or a blockage.. It appears on 3 Remeha models in our database.
Technical description: Max.water temperature: Flow temperature too high.
What causes the Remeha 1 8. fault?
This fault occurs when the water leaving the boiler exceeds its safe temperature limit, causing the system to shut down for safety. The most common cause is a failed internal pump that isn't moving water away from the burner quickly enough, or a significant blockage within the heat exchanger that is restricting flow. It can also be triggered by a faulty sensor that is incorrectly reporting the water temperature as being too high.
This issue is more frequent in autumn when heating systems are switched back on after a long summer break, as internal pump components are prone to seizing during periods of inactivity.
DIY fix possible
Check that all radiator valves are fully open to allow water flowEnsure the boiler pressure gauge is between 1.0 and 1.5 barPress the reset button once the boiler has had time to cool down
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Gas Safe Register →Remeha models that show the 1 8. fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Remeha 1 8. 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