High
Power ON LED (Green) blinking on Halstead Ace High

Your boiler has detected that there is either not enough water inside the heating system or the sensor responsible for detecting flow is not operating correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Indicates a fault with the water pressure or flow switch (primary flow switch contacts open).

From this model's manual
Verified against the AceAceHigh20Manual installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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