Worcester Bosch Greenstar 4000

In essence, if you have the heating on and then you turn on a hot water tap, the heating goes off for several minutes after you have turned the hot water tap off. It can be up to 5 minutes before the heating comes back on. Is this by design? I can see why the heating goes off when the hot water is required, but to stay off for 5 minutes once the hot tap has been turned off seems a bad design and an inefficient heating process to me.