High
F1 on Glow-worm Ultracom sxi

Your boiler is failing to light because it cannot detect a flame, meaning you currently have no heating or hot water.

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

Ignition failure

From this model's manual
Verified against the Glow Worm Ultracom 2 Sxi installation & service manual, page 41.
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 temperature sensor inside your hot water storage tank detects that the water has dropped to a near-freezing level. To protect the internal components from being damaged by expanding ice, the boiler temporarily pauses operation until the water temperature rises to a safe level. This is typically caused by extremely cold incoming mains water or a storage tank located in an unheated area like a garage or loft.

This fault is almost exclusively seen during the winter months when external temperatures drop significantly and reduce the temperature of the incoming mains water.

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 F1: 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