Medium
A4 on Viessmann Vitodens 242-F FB2B

Your boiler has detected that the water pressure inside your central heating system has become too high, which can put unnecessary strain on the internal components.

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

Max. system pressure exceeded

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.

DIY fix possible

Locate a radiator in your home that has a bleed valvePlace a cloth and container under the valveSlowly open the valve to let a small amount of water out until the pressure gauge on the boiler drops back into the green zoneEnsure the valve is securely closed once the pressure has normalized

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 A4: 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

A3View →F2View →

Related guides you might find useful

Boiler keeps losing pressure

Six most common causes of dropping pressure.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →