Posting here as Edugeek is well indexed by Google and this might be of help to someone with a boiler problem.

Symptoms:

The fan of a Worcester 24i combi boiler intermittently cuts out. This causes the fail-safe to trigger and the boiler to shut down, and the water runs cold. The fan may restart, the boiler might re-ignite, but cuts out again and the fail-safe shuts down the boiler.

Plumber says the best case scenario is a new control board (£150), worst case is a new boilder (>£1,000).

I wasn't having any of that so I thought I'd try and fix it. I found the fan fault was caused by a relay burning out.

The relay you need is

DPDT power relay, 5A 24v DC

Man Part No G2R-2 24DC

The RS stock number is 366338 http://uk.rs-online.com/web/p/non-latching-relays/0366338/

The relay costs less than £5.

You will also need a soldering iron and a solder-sucker.

DISCONNECT THE MAINS POWER! Electrocution can spoil your day.

Make a note of the power connections to the main board.

Remove the metal board cover and remove the circuit board (very fiddly task)

The fan is controlled by a relay, circled in the photo below

De-solder the relay by removing the solder on the 8 joints shown in the photo below

Solder the new relay into place, reconnect everything.