Central Heating stuck on

[Paulmark]

Boiler is Vokera 20/80 R.S. Flowmatic combi, approx 11 years old. Switched on central heating yesterday, first time in months. Bled all radiators although hardly any air found. 3 out of 10 radiators took over 4 hours to warm up and only after turning down the other 7. Water pressure is ok on the boiler. Switched heating off last night via control unit, but several hours later realised radiators were still warm and heating was still on. Can anyone offer any advice?

 

[Softus]

Do you still get decent hot water from the taps?

Does the pump run?

If so, the problem is likely to be a sticking divertor valve.

Or, but less likely, an accumulation of gunge restricting the flow at a crucial point in the system.

 

[Paulmark]

Do you still get decent hot water from the taps?

Does the pump run?

If so, the problem is likely to be a sticking divertor valve.

Or, but less likely, an accumulation of gunge restricting the flow at a crucial point in the system.

Thanks for feedback Softus.
Yes, still getting decent hot water from taps. Sometimes central heating will not turn off, so I turn thermostat down on boiler and some hours later system cools down. Today I could not switch bolier on, although still receiving hot water and I can hear fan constantly running inside boiler. Shall read up on divertor valve.