Your problem is most likely going to be either a zone valve or diverter valve on your system, check that it is opening, if there was a problem with your boiler it would not give you any heating either. If the valve is not opening you will see a lever on the casing move this to the manual position and lock it there and this should sort out your problem and if it works check there is power from the cylinder stat if there is it is likely to be the synchron motor on the valve these can be changed on most valve types.
Jimmy Gas
December 2006