I am building a new house and intend to use an air source heat pump to provide the domestic hot water and the underfloor heating. Top of the list so far is the Mitsubishi Ecodan. (It's cheap and I live in the Shetland Islands so getting an engineer in for something that isn't available locally is a big expense).

My question is about the controllability of the Ecodan. I have read the installation guide and the manuals for the controller that come with it. Mitsubishi seem to recommend that to keep the electricity bills down the controller is set to run the machine during the night when electricity is cheap rate. All very sensible but what about the times when a boost to the DHW is required? As far as I can see there is no "boost" button anywhere to run the machine for, say, an hour to boost the hot water tank. The only way to do this would be via a traditional immersion heater boost function. This seems a waste as the heat pump would obviously be cheaper than the immersion heater, particularly during the day.

Am I right or have I missed something?

Thanks
Andrew