BoilerFaultCodes.com
AL34 High Lockout

Your boiler has stopped working because the fan that clears away waste gases is not spinning at the correct speed or its signal isn't being picked up by the system.

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: Fan tacho signal fault

What causes this fault?

This fault occurs when the boiler's internal computer tries to spin the fan but doesn't receive the correct feedback signal to confirm it is moving safely. The most common reason is that the fan motor has physically burnt out or the delicate electronic sensor inside the fan has failed, preventing the boiler from safely venting waste gases. In some cases, it can also be caused by a loose connection or a fault on the main control board failing to process the signal.

Typical repair cost £180-350 (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 AL34 — 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.

Vokera Unica HE 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