BoilerFaultCodes.com
29 High Lockout

Your boiler has detected an internal electrical fault with its gas control system and has shut down as a safety precaution.

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: Gas valve relay faulty

What causes this fault?

This fault occurs when the boiler's main control centre detects that the internal switches responsible for operating the gas valve are sticking or failing. The most common reason is that the electronic components on the circuit board have worn out over time, preventing the boiler from safely controlling the flow of gas. Because the boiler can no longer verify that the gas will turn off when it should, it shuts down immediately to ensure your safety.

Typical repair cost £250-450 (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 29 — 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.

Could it be time for a new boiler?

If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.

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