Yes.
When the hot water tap is turned on, the boiler runs similarly to when the central heating is on, but the gas heated water only circulates around the boiler (via the plate heat exchanger) rather than around the radiators. Cold mains water also enters the boiler and passes through the other side of the plate heat exchanger, and exits the boiler as hot water. The plate heat exchanger keeps the boiler water and mains water separate, but allows the heat to pass from the one to the other.
Anon, January 2015
