Hi I am not sure what boiler you have, but presume you mean you have turned the heating off at the programmer? When draining the system, you may have reduced the pressure in the whole system, so the boiler will not come on as the pressure will be too low. If this is ok then you may as well switch the heating on and control it by the room thermostat, it does not matter if it is on or off if you have taken the rad off, anyway with this fine weather it should not come on anyway.
john B
July 2008