Hi, The boiler is 2004 the actuator is a HONEYWELL VC4613-3 which I think has the cartridge 87161051320.
Do you think its worth me getting a cartridge and giving it ago. I will say thank you, as what you have said has made it all alot clearer to me now. All my reserch leads to what you have said.
Thanks.
Paul
January 2010