F.436 High

Viessmann F.436 Fault Code

Also written as F436 — same fault.

The Viessmann F.436 fault code means: your boiler has detected an electrical fault with the sensor that measures how fast water is moving through the system, causing the unit to stop working to protect itself.. It appears on 2 Viessmann models in our database.

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.

Technical description: Control mode | Short circuit, flow sensor
Typical repair cost £180-300 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Viessmann models that show the F.436 fault code

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

Source

Viessmann F.436 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 7 July 2026