On Pcb marked RL1(Relay) needs changing.it is clear body sealed unit.
Relay1( one) clicking,Not expansive
part no is .... OMRN G2 R2 24v dc .... (Relay).
search web From £5 to 25 Part price .
soldering is easy if u cando yourself,It cost me 3.50.incp&p.
Pcb is located at bottom near controls,screws,wire connections to dismantle.use commonsense.

AL -

PLEASE RE-CONFIRM PART NO. AND CLARIFY IF WORCESTOR PART AS I CAN NOT FIND WITH NUMBER PROVIDED ON GOOGLE. ALSO CHECKED RS SPARES ONLINE AND CPC TO NO AVAIL - THANKS

Martin, January 2009

Just got one off ebay (don't know why I didn't think to look sooner - typed in "omron relay" and got loads of options) Item number was 280309648996 if that helps

Tony C, February 2009

I have the same problem and a work colleague has found the right relay online in America but looking for a UK stockist at the moment - I'll post again when I know more

However I have noticed that, in my instance anyway, by undoing the screws holding the bottom section of the boiler front up and allowing it to drop forward until it lays flat, the relay has stopped chattering. Is a quick fix for me at the moment anyway

Tony C, January 2009