Will a worcester combi boiler need water in the heating system,to heat the hot water?

Yes, boiler services right, and also due to the boilers water to water plate heat exchanger, the boiler requires the primary heating system to be at min fill pressure as it uses this to heat your cold water to hot!! boiler will just lock out,until its done. 1. leak on system 2. pressure relief valve 3. main heat exchanger cracked and loosing system water out condensate! 4. expansion vessel failer of operation split diaphragm post job get gas safe guy out

Yes it will as the pressure sensor for the central heating will not allow the boiler to fire up if pressure is low due to no water.