BoilerFaultCodesYour boiler has shut down because there is a significant difference between the water temperature leaving the boiler and the temperature returning to it, usually caused by a circulation problem.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety switch-off: Temperature spread too large
What causes this fault?
This fault occurs when water is leaving the boiler much hotter than when it returns, which suggests the water isn't moving through your radiators quickly enough. The most common reasons are a failing internal pump that can't push the water effectively or a blockage caused by a buildup of sludge and debris in the pipework.
This fault is more frequent in autumn when the heating is turned on for the first time after summer, as pump components can seize or sludge can settle during periods of inactivity.
DIY fix possible
Ensure all radiator valves (TRVs) are fully openCheck that the boiler pressure is between 1.0 and 1.5 barBleed your radiators to remove any trapped air
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like F.23 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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