@alfapat 

So the problems you have are that your house has a large heat loss (Im assuming it is a big house), your system was designed to run at a high temperature (50C at -4C OAT) and it may not have been designed in the most efficient manner (possible buffer tank)

By way of comparison my current heat curve is 34C at 17C OAT and 40C at -2 OAT. My SCOP is 4.2 whereas your is estimated at 2.7. That means for every kWh of electricity we use over the year, I get 4.2 kWh of heat and you get 2.7 kWh of heat. You can see how that stacks your bill up quite a bit. A SCOP of 3.6ish is cost parity with gas heating.

If I were you I would try the following measures in order of increasing cost to try and improve the situation.

1. Try to lower your heat law curve, but not so far as you feel the rooms are not hot enough

2. See if you can access any cheaper heat pump electricity tariffs

3. Improve the draught proofing on your house (an infra red camera will help, they can sometimes be borrowed from your electricity supplier)

4. Improve house insulation, especially in the rooms in which you spend most time

5. Add bigger/ extra radiators especially in rooms in which you spend more time. It may be possible to change your biggest for a bigger one and then shunt the others to different rooms with smaller radiators

6. Get in an expert to see what can be done with system design. I would recommend an Elite Heat Geek, but I cant find one in your area. If you can get rid of the possible buffer and maybe use anti frost valves, that will improve efficiency. Occasionally though a buffer tank is needed.

7. You have a large electricity use and solar panels may help in the non-winter months, but when you need the most electricity they wont be much help. A very large battery however would allow you to store cheaper electricity and use it to power your heat pump. Octopus Cosy is a tariff which may be useful along with others. You will need to do some sums though to work out if it is worth the investment.

*Addendum

One other thing I just thought of that could help at a relatively low cost. Have a look at Homely which takes over control of you heat pump and learns to use it in the most cost effective way. I have heard good things about it.

Many thanks,  I haven't sent the Room radiator sizes , I thought I had.

However I shall look at the various ways you have suggested . Iam already on Octopus cosy as I have said I am trying to up the heating or should I say use the triple low peak periods.

Not easy to see where that is going but its averaging .24 pence since I set it up 2 days ago. 

I have in total spent on this house system including insulation at least £26.000 so now that I have retired I may have to take the hit but try tweeking a little.

I have just dropped from 50 to 42 and monitor it . Ill send radiator sizes which have been calculated 8 years ago when the system was installed . 

Space heating on EPC is written as 29,594 Water heating 3,023 . Not sure if thats helpful.

@alfapat So the EPC pretty much matches the heat calculation.

By all means tweak and see it that helps. If it doesnt then try to look at any upgrade costs as an investment that should pay back and some in a year or more (maybe 10 for a battery).

Looking at your radiator specifications, they look nice and large, are they single or double (or triple) radiators. I also note that they have TRVs which isnt the best way to run a heat pump, especially if using Water Law. Open the TRVs to max and use the lockshield valve to get the temperature you want in that room. Its quite trial and error and you may have to tweak several times. I would start with the room you want hotest, open it to full and work around that.

I also noticed that you have a 3 bedroom house, so not so large that you should have a massive heat loss. Can you describe your insulation a bit more. ie is the loft insulation 300mm thick etc.

Can you send me your latest electricity bill too so I can check your usage.

Cosy is pretty good but avoiding the peak period can be tricky, if you have a lower average unit price though its a good start. Are you considering getting an EV? Ownership opens up a whole new range of cheap overnight tariffs. Very useful with a large home battery.

So when you talk about the lockshield valve , is that the TRV on the entry side , I would have thought they are always wide open , unless you meed to move the rad. All my bedrooms are on about between 2 or 3 , batroom 5 max Kitchen always coldest at max , Large lounge most used on max, cant say what inlets are positioned , perhaps these are nthe one you suspect are not open fully.

Roof above ceiling and between joist 300mm a double layer. Radiators all double panel.

Latest full month from EDF Heat pump tariff was 23Nov. - Dec 22 £452 /1925Kwh

Octopus started 30th Dec. - 6th £151.76 5 of those days on COSY 595.346N KWH total

Definitely cannot afford EV. I have been advised by potential installer (not made up my mind yet on quote ) that OCTOPUS gO can be for charging home batteries or EV. There are two GO tariff's so both are 7p at night and 15 eport cant remember standard.

Hope that helps ....PHEW#

@alfapat The lockshield valve is the one opposite the TRV. Heat pumps dont play well with TRVs and they are not necessary when using water law. Just set all your TRVs to maximum. Here is an article on how to adjust the lockshield valve to get the right temperature in the room.

https://renewableheatinghub.co.uk/how-to-balance-radiators-the-role-of-the-lockshield-valve

The bill is eye watering, but im having difficulty understanding why you need so much heat with what appears to be good insulation. Are your windows double glazed? Could you post a couple of pictures of your house and outside heat pump unit please.

If you can get GO without an EV then that will be very helpful with a large battery, but I think we need to get to the bottom of where your heat is going first.

This is one of the best value batteries on the market but you will need to get it installed.

https://www.fogstar.co.uk/products/fogstar-energy-15-5kwh-48v-battery?gad_source=1&gclid=Cj0KCQiAvvO7BhC-ARIsAGFyToV0_nJWYp_1bRQ4k0KChIry5lgqNtE1dkMl9ZgiGMYdY-TREkPN6ycaAqalEALw_wcB

I have two pics front and rear to hand, also think its a good idea to look at out going temps .I was looking at infra red  but a bit confused , perhaps wired and taped like 12 needed , dont want to over spend.

YES , windows doub;e glazed. Heat pump in pic to rear North Facing.

I can get better ones tomorrow if required but thse were for Solar Quotes.

Two rads including Shower Roomand Kitchen almost a full turn to open fully.

@alfapat Im even more confused now as looking at the house I wouldnt have guessed more than 8kW would be needed. Thats not an exact science I know but Ive become pretty good at guessimating.

You can go to the trouble of measuring incoming and outgoing flow temperatures to the radiators but you can get a pretty good result just by tweaking a bit and retweaking.

I think a better place to start would be to strap some temperature probes to the heat pump flow and return and the buffer cylinder flow and return. Im becoming increasingly convinced that the issue must be with the system design. My bungalow isnt that much smaller than yours, of older construction and manages well on a 5kW heat pump!

You dont need to spend a lot, something like this will be fine, just zip tie the probe to the bare pipe and replace the insulation over it.

Are your walls twin skin with a cavity? Is there any cavity insulation?

Ordered probes. Did you get EPC report that gives the floor area and more . 

@alfapat No it wasn’t attached to the email. Can you resend it please. 

@alfapat It is larger than it looks at 200+ m2 but didn’t you say that was the old EPC before the insulation improvements? 

Im just struggling to see what else you could reasonably do to insulate better. Even the size it is 16 kW feels too large to me. 

@bontwoody Yes , EPC was 2015 before HP was installed.

I have sent a planof house layout and build descriptions , not an expert on details given , but some insupation included.

Sorry "Insulation"