Rdiators warm when central heating off

[BazzaS]

I've a Worcester 4.5 combi boiler for both hot water and central heating. The boiler settings are 'On' for hot water (= on all the time for on-demand supply); 'Twice' for central heating (= on for a couple of hours in the morning and in the evening). Recently I've noticed that the radiators are warm during the period when the central heating is off - and I don't mean just after it's gone off i.e. latent heat from the 'on' period. When this occurs I've checked that the central heating setting is indeed 'off' at the boiler. The radiators each have their own thermostat - all of which are at the middle setting. The boiler is serviced annually.
I would have expected the radiators to be cold during their 'off' period so this behaviour seems odd - do I have a problem ? If so what is it likely to be?
Thanks

 

[BazzaS]

Just a bit more info - the radiators aren't always warm between central heating 'on' periods - infuriatingly inconsistent !
Regards
Bazza

 

[OilLecky]

Bazza, I don't know this boiler but the oil fired Worcester Heatslaves can get a problem where the diverter valve stem sticks down, thus supplying the rads when they should be off. If your boiler is similar, the electrical head of the valve can be removed from the valve and operated to make sure that it works. If you can pull up the valve stem by using pliers GENTLY on the pin in the valve then it was stuck down. The valve cartridge can be replaced quite easily.

 

[mlcinfl]

Are the rads getting hot, or just slightly warm?
If slightly warm then it could simply be the boilers pump over-run dumping hot water from the heat exchanger into the system when hot water demand ceases.

 

[BazzaS]

Mlcinfl,
Sometimes they are hot but mainly they are warm.

 

[mlcinfl]

Mlcinfl,
Sometimes they are hot but mainly they are warm.

It sounds to me that the diverter valve might be faulty.
Good luck.