High
A8 on Viessmann Vitodens 242-F FB2B

Your boiler is struggling to push water through the system, likely because there is trapped air or a blockage preventing proper flow.

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

Air lock in the internal circulation pump or minimum flow rate not achieved

From this model's manual
Verified against the Viessmann Vitodens 242 F B2ua installation & service manual, page 128.
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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Related fault codes

A9View →F4View →

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