Worcester 240 Boiler Cut Out Fault

[RobCarter]

My Worcester 240 Boiler has developed a habit of cutting out. When the red cut out switch is depressed the boiler fires up again and operates normally for another few hours.
The pattern seems to be that it only cuts out when the boiler is lit for a longer period (e.g. later in the evening or at weekends when the central heating has been on for some time).
I had a new Gas Valve fitted a couple of months ago but all seemed well for several weeks until this problem started.
Doubt it's relevant but the combi boiler only serves the cental heating to the house and hot water to utility room and an infrequently used shower room. Main hot water supply is from a gas AGA.
Any ideas as to the cause of the problem would be very much appreciated.
Thanks,
Rob

 

[Andygasman2010]

This red cut out switch, is it on top of the boiler? I pressume it's intermittantly overheating then. If so, there's lots of things it could be. Mucked up system, dodgy pump, boiler stat failed.... What's the system pressure like?

 

[sourcebranch]

Could be as simple as the oh stat. Have known these to become weak over time??

 

[combispecialist]

if this is the model with the paddle flow switch they have an issue with sticking intermittantly after the hw turned off,causing o-heat