BoilerFaultCodesYour boiler is performing a routine self-test of the fan speed and it is not necessarily a permanent error code.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: The fan should reduce to 1200 rpm which will flash ‘12’ on the LCD display.
What causes this fault?
This code appears when the boiler’s internal computer performs a routine check to ensure the fan can safely slow down to its minimum required speed. It is often a temporary status message triggered during a self-test rather than a mechanical failure. If the code stays on the screen, it suggests the fan is struggling to reach the correct speed or the control board is failing to read the sensor data correctly.
DIY fix possible
Wait for the boiler to complete its internal test sequenceIf the '12' remains or repeats indefinitely, try resetting the boilerCheck for any visible obstructions at the external flue terminal
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.
Affiliate links — we may earn a commission at no extra cost to you.
Glow-worm cxi / csi range 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.