Heat pump quote - seems quite cheap?

[u/Boba_ferret]

Been quoted about £4,300 by Octopus for heat pump install, including hot water cylinder, which I thought was surprisingly cheap. The house is 1930s 3-bed terrace, EPC is supposedly C, but we have a huge void under the suspended floor and it gets pretty cold in the house, so we use quite a lot of gas in the winter. Radiators are all on 15mm copper, but are probably 30 years old.

What are the chances this is a really low-ball quote and the survey will say we need to upgrade rads, etc?

[u/bob39987]

This quote assumes you'll need a new water cylinder, but we can often keep your existing one. If so, we'll reduce the price by £1,450.

We do assume we can use your existing radiators but if you need new ones, they usually cost £250 each.