High
b18 on Ideal Imax W

Your boiler is temporarily pausing because it is struggling to move water through the system, often due to a blocked filter or a trapped air pocket.

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

Blocking code (appears alternating with 9)

From this model's manual
Verified against the Ideal Imax W installation & service manual, page 50.
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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