27 High
Your boiler has detected that water is not moving through the system quickly enough to prevent it from overheating.
Technical description: Insufficient primary flow
Typical repair cost: £120-£350 (including labour)
DIY fix possible
Check that all radiator valves are fully openEnsure the external heating pump (if visible) is runningCheck that the system water pressure is within the green zone on the gaugeReset the boiler using the selector switch
Protect yourself from future repair bills
A boiler cover plan would cover faults like 27 — no call-out fees, no surprises.
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Parts commonly replaced
- External circulation pump
- Flow/Return thermistors
- System filter (cleaning)
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