Extending a property with an ASHP and underfloor heating

FreeBear

If you only need 4000kWh pa (according to the EPC), I'd say a 9kW heat pump has a fair bit of spare capacity to heat a modest extension. But you'd need an expert to look at the figures to confirm.

akwexavante

As part of the purchase process, i'd want to try and get the seller to have the ASHP serviced. It should be still under warranty at that age if it has been serviced every year since installation.  It's not unreasonable to ask the seller if the heating system is working and request proof that it is.

If it hasn't been serviced, then any remaining warranty may be null and void.  If the warranty has expired because it hasn't been serviced, then me's thinks that that theirs room for a reduction is the price of the house because you're buying a house with an expensive heating system that cannot be proven to be working and or safe to use and without any warranty.

Finding an ASHP service engineer isn't difficult, just google them in the area where the house is. They'll be a small number to choose from.  More and more younger gas engineers are training to service ASHP's now.

I've extended my house and added two radiators with no ill effect and no bill increase of note.