Scolding water but no heating

Oil Boiler : Boulter Economy 50/70, 8 Rads

We recently moved into a bungalow which was stood empty for 6 months. The water would heat to scolding temperature (turning down the thermostat on the immersion tank didnt make any difference), but the radiators didnt work (2 or 3 would get luke warm). We noticed the boiler would only come on for short periods (5 mins) then switch off. We thought it was because it had been stood for so long so let it run for a few days, and it did work, we had all hot radiators and hot water (still too hot though). It worked fine for 4 weeks, until now, its gone back to the way it was.
Things I have noticed are, the pump is still whirring away hours after the system has shut down (I think its permanently going!) and the boiler comes on every 20 minutes or so for about 5 mins even when the system is off.
Thankyou for looking and hope someone has an idea.

Have you checked the three port valve ?

See FAQ section

Thanks for your reply outinthestix. From your reply I've managed to get heating again!
The system doesnt have a 3 way valve, it has two 2 way valves. I'm not sure how to test them, but I switched one to 'manual' and we have hot radiators again!
Probably a really stupid question, but does that mean that particular valve is knackered, or could it still be something else?
And is that why the water was overheating?
Cheers

change the head (actuator) of the one you set to manual and then you will be fine and dandy

just make sure you get exactly the same one then changing over will be easy