BoilerFaultCodesYour boiler has detected that water is struggle to circulate through your heating system quickly enough, often due to a blockage or a pump issue.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: High Flow/Return Differential
What causes this fault?
This fault occurs when the water temperature leaving the boiler is significantly higher than the water returning, suggesting that heat isn't being moved away fast enough. The most common cause is a restriction in the system, such as a build-up of sludge in the heat exchanger or a failing pump that can no longer push water through the radiators effectively.
This issue is most frequently seen during the first cold spell of autumn when the heating is turned back on after sitting idle for several months, often causing the pump to seize.
DIY fix possible
Ensure all radiator valves (TRVs) are turned to the highest settingCheck that the boiler pressure is between 1 and 1.5 barBleed all radiators to remove trapped air from the system
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A boiler cover plan would cover faults like P5 — 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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