Sizing heat pump

I am having quotes for replacing a cheap underperforming ASHP. My house is approx. 175-180m2 with full insulation and d/g. I have 14 oversized radiators. I just need a rough idea about the size and quality of the HP'S I am being quoted for. I am looking at installing either a Mitsubishi Ecodan or a Panasonic Aquera. The HP is tanked into an ACV SMART SLME300L. tank at present. Some installers are saying I should replace it and others are saying its fine. Any suggestions would be appreciated as to the sizing of the system, the compatability of the tank and the quality and reliability of the Mitsubishi and the Panasonic.

The size of a heat pump for your property can only be calculated once a full survey has been done and heat losses determined.
How do you know that your radiators are oversized. Are they oversized with a 50K dt or a 30K dt?

The DHW cylinder needs to have the control sensor located to suit the control logic of the attached heat pump to gain the best efficiency. If your existing cylinder is not compatible with the Ecodan or the Panasonic then it will not heat to it's most efficient.

As with any manufacturer, there are those that like the brand and those that do not. Choice of equipment is subject to the same considerations as you would adopt when buying a car.

As for reliability, all of the systems out there are mechanical pieces of equipment and subject to failure based on the engineering standards employed in the factories, together with the care exercised when being installed, and providing that the design and selection has been carried out correctly.

Ask your contractors for references and talk to the people who have had systems installed by these companies.