Hi Foggy,

Our gas boiler is 20+ years old and deemed obsolete, and I was struggling to obtain a new heat exchanger. Fortunately my wife managed to locate a second hand boiler for sale, with the required part still in good condition. So we got the spare part at a fraction of the cost of a new one, and I managed to get the boiler back in operation, which pleased my wife no end.

Before I recently installed the A2A ASHP, I had a 2kW electric convection heater in the hallway, which I also had connected to the diverter. When the hot water was up to temperature and the immersion heater switched off, the the excess energy from the solar PV was diverted to this heater to assist the gas boiler in heating our home. By doing this we reduced our gas consumption by 20% over a year.

I had though about getting an electric storage radiator to store solar PV energy for use at night, again to reduce gas consumption. I may do so at some time in the future.

Posted by: @derek-m

Before I recently installed the A2A ASHP, I had a 2kW electric convection heater in the hallway, which I also had connected to the diverter. When the hot water was up to temperature and the immersion heater switched off, the the excess energy from the solar PV was diverted to this heater to assist the gas boiler in heating our home. By doing this we reduced our gas consumption by 20% over a year.

I had though about getting an electric storage radiator to store solar PV energy for use at night, again to reduce gas consumption. I may do so at some time in the future.

That's quite a novel use of storage heaters.  But maybe yours it's the sort of hybrid approach needed where gas is still used but consumption is reduced.  A bit like hybrid cars, where we have fossil fuels assisted by, rather than replaced by, electricity.     

On costs, I've recently been spending some quality time on Alibaba.  Typical examples (clickable links):

11kW ASHP monobloc - $838

Heat pump water cylinder - $286

Radiator-style fan coil unit - $125 (includes 'smart' TRV)

To that you would add VAT, import duty (2% for the fan coil, 0% for the others), and sea freight (a few hundred dollars for a part container load, although the market is a bit crazy at the moment - it gets cheaper per unit if you can pack out full containers).  But let's say all-in you'd get change from £1500-2000, depending on how many fan coils you want.  This price doesn't include pumps, valves or expansion vessels, which are standard central heating parts (a few hundred pounds).

And then installation is basically 'running some pipes' and 'adding a circuit to your consumer unit'.  Since it's monobloc there's no f-gas to worry about, and the install is something any plumber can do (it's roughly the same amount of piping as a new gas boiler system).  The electrical side is probably ballpark £250 depending on your CU setup and exactly where it's going.

Now I absolutely cannot vouch for quality, veracity of suppliers, or believeability of these prices.  I very much expect they will go up somewhat when you talk to the supplier (for instance I talked to the fan coil supplier and the price for that unit was $156 not $125 as listed).

But it doesn't half make you think.