BoilerFaultCodesYour boiler has detected that the water is heating up too quickly or isn't circulating properly through the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Difference between the flow and return temperature is too high, sensor error or insufficient circulation.
What causes this fault?
This fault occurs when heat isn't being moved away from the boiler's internal heat exchanger fast enough, causing a rapid temperature spike. The most common reasons are a failing circulation pump, a blockage in the system pipework, or air trapped within the unit preventing water flow.
This issue often surfaces during the first cold snap of autumn when the heating is turned on after being dormant all summer, which can cause the pump to seize.
DIY fix possible
Check that the boiler pressure is between 1 and 1.5 bar on the gaugeEnsure all radiator valves are fully openCheck for any visible leaks around the boiler or pipeworkRestart the boiler using the reset button
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like H.01 – .05 — 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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