BoilerFaultCodes.com
12 High Lockout

Your boiler's control panel has likely detected moisture or dampness inside the screen or buttons, preventing it from working correctly.

Call an engineer soon

Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: USER INTERFACE: INTERFACE MAY BE DAMP. DRY IT OUT OR REPLACE.

What causes this fault?

This fault occurs when the boiler's control panel detects moisture or condensation within the electrical circuits of the display screen. The most common reason is water ingress from a leak elsewhere in the boiler or high humidity causing dampness behind the buttons. When this happens, the interface becomes unresponsive to prevent a short circuit, resulting in a system shutdown.

Typical repair cost £120-280 (including labour)

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 for a qualified engineer in your area.

Gas Safe Register →

Protect yourself from future repair bills

A boiler cover plan would cover faults like 12 — no call-out fees, no surprises.

Top rated
OpenFix
Boiler & heating care plans
Get a quote →
Hometree
from £12.95/month
Get a quote →
HomeServe
from £8.00/month
Get a quote →

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

Glow-worm Xtramax is discontinued — time for a new one?

Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.

UK's #1 online installer
Boxt
Fixed-price online quotes. Next-day installation.
Get a free quote →
Heatable
Instant online boiler quotes from £1,499.
Get a free quote →
iHeat
Fast installation. Price match guarantee.
Get a free quote →

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

Related fault codes