BoilerFaultCodesYour boiler has shut down because water isn't moving through the system quickly enough, causing it to overheat too rapidly.
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: Temp. spread too large - Temperature spread too great. Water circulation too low
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water is heating up too quickly or that there is a massive temperature difference between the pipes going out and coming back. The most common reason is a blockage or a failing pump preventing the water from circulating through your radiators. It essentially means the heat being generated has nowhere to go, so the boiler shuts down to prevent internal damage from overheating.
This fault is frequently seen at the start of autumn when heating systems are turned back on after being idle, as pump components can seize or sludge can settle during the summer months.
DIY fix possible
Check that all radiator valves (TRVs) are turned to the highest settingEnsure the boiler pressure is between 1.0 and 1.5 bar on the digital displayCheck for recent air locks and bleed your radiators if they have cold spots
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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