Medium
F.456 on Viessmann Vitodens 200-W B2KE-25

Your boiler found a problem with its status when it tried to start up, so it may have stopped or refused to light, but this is usually fixable by a qualified engineer.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

System status at system start

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 100 W Wb1a 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like F.456: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

F.22View →F.23View →

All 170 fault codes on the Vitodens 200-W B2KE-25

Seeing a different code? Every code this model can display, in one place.

F.7F.8F.9F.10F.11F.12F.13F.14F.15F.16F.29F.30F.49F.50F.57F.58F.59F.62F.63F.65F.67F.68F.69F.70F.71F.72F.73F.74F.77F.89F.91F.92F.93F.94F.100F.104F.142F.160F.161F.162F.163F.182F.183F.184F.185F.299F.342F.345F.346F.348F.349F.350F.351F.352F.353F.354F.355F.357F.359F.361F.365F.366F.367F.368F.369F.370F.372F.373F.375F.377F.378F.380F.381F.382F.383F.384F.385F.386F.387F.388F.395F.396F.399F.400F.401F.402F.403F.404F.405F.406F.408F.410F.416F.417F.418F.425F.426F.427F.428F.429F.430F.432F.433F.436F.437F.440F.441F.442F.443F.444F.445F.446F.447F.448F.449F.450F.451F.452F.453F.454F.455F.457F.458F.461F.462F.463F.464F.467F.468F.471F.473F.474F.517F.527F.528F.530F.538F.539F.540F.542F.543F.544F.545F.546F.547F.574F.575F.576F.577F.578F.579F.580F.581F.582F.666F.667F.668F.669F.670F.671F.672F.673F.682F.683F.684I.55I.56I.57I.59

Related guides you might find useful

What pressure should my boiler be?

1 to 1.5 bar when cold on most UK boilers, from the manuals.

Read →

Boiler keeps losing pressure

Six most common causes of dropping pressure.

Read →

Low pressure: how to repressurise

Step by step using the filling loop.

Read →