BoilerFaultCodesYour boiler has detected that the water is circulating or heating up incorrectly, likely due to a pump issue or a blockage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow/return sensor temperature test.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water is not moving through the system quickly enough to carry heat away from the burner. The most common reason is a failing circulation pump or a blockage within the heat exchanger caused by a buildup of sludge and debris. Essentially, the boiler is shutting down to prevent itself from overheating because the water has become trapped and is heating up too fast.
This issue often comes to light during the first cold snap of autumn when the heating is turned on after being stagnant all summer, causing internal pump parts to seize.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like E154 — 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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