High
5x on Vokera Syntesi 25

Your boiler's central computer has encountered an internal error and can no longer control the heating or hot water safely.

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

Fault codes 5x appear if a problem with the main board exists.

From this model's manual
Verified against the Vokera Linea He 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.

What causes this fault?

This fault occurs when the boiler’s main control board suffers a critical electronic failure or loses communication with its internal sensors. It is usually caused by age-related degradation of the circuit components or a sudden electrical surge that damages the board's memory. Because the 'brain' can no longer guarantee the boiler is operating safely, it shuts the entire system down as a precaution.

While this can happen at any time, it is slightly more common during stormy weather when power surges or lightning strikes can cause electrical damage to the sensitive circuit board.

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.

Find a Gas Safe engineer
Search the official register →

Avoid the next call-out bill

A cover plan would handle faults like 5x: 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

Related guides you might find useful