425 Low

Viessmann 425 Fault Code

The Viessmann 425 fault code means: your boiler is having trouble connecting to the internet to set its internal clock, which may disrupt your heating schedules.. It appears on 1 Viessmann model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Time synchronisation failed
Typical repair cost £0-60 (including labour)

DIY fix possible

Check your home Wi-Fi router is switched on and workingMove your router closer to the boiler if possible or check for signal interferenceOpen the ViCare app on your phone and follow the prompts to reconnect your boiler to the network

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like 425: 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.

Viessmann models that show the 425 fault code

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

Source

Viessmann 425 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