As others comments said, it depends on the climate :
The problem is that the power/performance of the heat pumps decreases with the cold weather and the necessary increase in the temperature of the heating water, which obliges to keep the boiler for the cold weather.
This is a problem for the heat pumps without probable solution and little progress to wait.
The solution is to insulate the house very well so that its needs can be covered by the heat pump with less hot water. Divide the losses by 2 at least.
