Go upstairs and into your airing cupboard. Assuming you have a typical central heating system. Look for two boxes with levers coming out from the top. Should be marked up as auto and manual I think.
Similar to this.
Anyway, you have one for hot water and the other for heating. Feel the pipes and see if you can identify which one is the heating. Try overiding the valve.
Classic component to fail, lack of usage normally causes the motor to burnout when the heating is switched back on after a long spell being off.