Heating is off, some radiators are still on!?

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Hello,

I recently moved into a victorian house that has had gas central heating fitted some years in the past. Now it's summer, I've switched off the heating side of it (but hot water still on obviously) to find that one of the radiators still gets piping hot (when the hot water is on) and another gets a bit warm. Not having a clue on how central heating even starts to work, I was hoping to get a bit of advice here. For instance, is the heating and hot water totally separate systems (but sharing the boiler) or is it one long pipe and controlled with valves and stuff??! (You get my level of understanding now!).

What I really need to know is whether it's something that could have broken since I moved in (Jan '04) or it's more fundamental, like an incorrect installation.

Many thanks for any advice you can give. I can try and give more info if needed.

Richard.

Additional: When I say I switched off the heating, I mean both at the thermostat and the timer.

 

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Looking on another site (diyfixit.co.uk) I found:-

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Warm radiators upstairs when the heating is off, and hot water is on

If this happens, it is probably because the check valve on a gravity fed system has failed. In a gravity fed system, the hot water cylinder is heated by water from the boiler which flows due to the gravity and not a pump. To prevent the water also heating the radiators when the heating is off, a check valve is fitted. If this has failed, the radiators upstairs will begin to receive some of the heat. The valve will need to be replaced by a heating engineer.
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Just in case anyone else finds this site via a search engine, as I did, and has the same problem!