I have a gas boiler that provides the heat for radiators and water. I
have an electronic timer that allows me to set two on and off times each
day. The boiler will run at those times if required and I can select
"off", "auto", "once" or "on" for heating and water separately.

My normal summer setting is "off" for heating and "auto" for hot water.

In the last week, I have noticed that the radiators are heating up when
the boiler is running, even though the controller is set to "off" for
heating.

I have no room thermostat, but each radiator has a thermostatic valve,
so I can turn them all off, but that isn't really the point. I want to
get things running smoothly before the winter comes.

I had the boiler serviced two weeks ago, but he just hoovered the boiler
out, checked gas pressures etc., so I can't see how he could have caused
this problem.

The only other components of the system that I can see are one motorised
valve (I'm not sure if that controls the water or the heating), and a
pump - presumably for the heating.

Can anybody suggest where the problem might be and whether I need to
call in professional help to fix it. I can do basic electrics and
plumbing, but I've never drained down a central heating system.

TIA

Steve