How much does it cost to fix Viessmann error code A1?

Typical repair cost for the Viessmann A1 fault is £80-150 including labour.

A1 High

Viessmann A1 Fault Code

Q: What does the Viessmann A1 fault code mean?

Your boiler has stopped working because the water pressure inside the system is too low to operate safely.

The Viessmann A1 fault code means: your boiler has stopped working because the water pressure inside the system is too low to operate safely.. It appears on 1 Viessmann model in our database.

Technical description: Burner blocked, water pressure too low

Typical repair cost £80-150 (including labour)

DIY fix possible

Locate the filling loop (usually a silver braided hose under the boiler)Open the valves to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 barClose both valves tightly and restart the boiler

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Viessmann models that show the A1 fault code

Click a model for the full fault code list and model-specific repair notes.

Vitodens 100-W Repair: £80-150

Source

Viessmann A1 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026