BoilerFaultCodesRemeha F/R ∆T = 45°C Fault Code
Also written as FRT45C — same fault.
The Remeha F/R ∆T = 45°C fault code means: your boiler has sensed that water is not circulating quickly enough through the system, so it has safely shut down to prevent overheating.. It appears on 1 Remeha model in our database.
Technical description: Low flow condition - boiler will shut off and not lockout
What causes the Remeha F/R ∆T = 45°C fault?
This fault occurs when the temperature difference between the water leaving the boiler and returning to it becomes too wide, indicating that heat isn't being carried away fast enough. The most common reasons are a failing internal pump that can't push the water through, or a blockage caused by a buildup of sludge and debris in the system. When the water moves too slowly, it lingers in the heat exchanger and risks boiling, triggering a safety shutdown.
This fault is frequently noticed at the start of autumn when the heating is first turned on after summer, as pump components can seize during long periods of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure the central heating pump is running and hasn't seizedCheck that the system pressure gauge is between 1 and 1.5 barBleed all radiators to remove trapped air
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Gas Safe Register →Remeha models that show the F/R ∆T = 45°C fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Remeha F/R ∆T = 45°C 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