Heat pumps take much longer to heat the system, to get it to the desired temperature. Combine that with a property that is not insulated to very high standard, and you get a heating system that is incapable of keeping you warm.
Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.
Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.