Boost turns off when using hot water

We only turn our heating on when it's needed, so we use boost maybe one hour sometimes 2 hours a day when it's very cold. I have noticed that if I start doing the washing up around the same time we use boost, the hot water is indeed hot but the radiators barely get warm and when I in fact stop using the hot water, the boiler turns off when I turn the tap off and boost never comes back on despite the hive app saying its still on. I was under the impression that a combi boiler should be able to do both at once? Our boiler is the Worcester Bosch Greenstar CDi Compact ErP