my heating works but no hot water?

sounds like an air lock in the system when the hot water circuit is included in the circulation. Check that you have air vents on both sides of your pump - one for CH and one for HW. These release trapped air from the very top of the system causing potential air locks to escape. The smallest of air locks will prevent the pump circulating and the boiler will lock out due to overtemp

tim
November 2009