BoilerFaultCodesYour boiler's internal fan isn't spinning fast enough to safely clear away exhaust fumes, causing the system to shut down for your protection.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Fan speed too low
What causes this fault?
This fault occurs when the boiler's control system detects that the internal fan is spinning slower than the required safety threshold. The most common reason is a buildup of dirt or mechanical wear within the fan motor itself, though it can also be caused by loose electrical connections or a failing control board failing to send the correct signal.
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 C1 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Worcester Bosch Greenstar 12i System 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.
Affiliate links — we may earn a commission at no extra cost to you.