Dillsue

Might be easiest to suck it and see by bypassing the accumulator with the flow pipe and replacing the scondary pump with a straight section of pipe. Avoid sharp bends/elbows in the accumulator bypass!

No idea about how NG operate but I emailed the SPEN area engineer who got a junior engineer to reply and we had a verbal agreement in a couple of days to double our existing 3.68kw G98 limit. Submitting the G99 form was just to formalise things...and take some cash off me!

Stupid of me to assume the air inside the house was damp when you mentioned rusting stoves and wok. I should have realised that you might keep your stoves and wok in the garden......no wonder the stoves don't heat the house if they aren't in it. I'm done here. Adios

All those damp issues will almost certainly be due to you not heating the place adequately. When you breath, wash or the plants in your avatar respire, moisture goes into the air. If the surfaces in your house are cold the moisture will condense as water and you'll get all the issues you mention. Again that's physics. All of those issues will cost you so that cost needs to be set against the cost of paying extra to heat the house.

That's way lower than I though but still meaningless to @zoothornas a numeric value.

A hole in a wall or an open window or door is uninsulated, everything else has an insulation value even if its low. That's physics. Your stone walls likely have a better insulation value than early double glazed windows

I think that is a recurring theme

Someone posted a link above to the Vailant controller manual which tells you what the moon symbol means.

Flow temperature is the temperature of the water coming out of the heat pump/boiler. The "medium number setting" would be whatever temperature your system was designed to run at...did you get any paperwork when the original heat pump was put in? If you want the best efficiency you want the flow temp to be as low as possible as that is where heat pumps are most efficient. If you run low temperatures you need bigger radiators to compensate for the lower temperature. In a high heat loss house like yours you'd need some pretty big rads to be able to run the heat pump at low temperatures for best efficiency. The size of rads question has been touched on earlier in the thread!

Isn't the Vaillant stat embedded in the controller which zoot is thinking of relocating.....already within the house?? Our LG is set up seemingly the same with the LG controller having a built in stat and a third party stat is wired to the outdoor unit. Isn't that similar to lots of HPs??

Im sure the easiest way forward for zoot is to relocate the existing stat/controller.....all terminals are know and visible to zoot so easy to replicate with a longer piece of cable. More importantly it's all at ELV!!!! @zoothornthe stat/controller wants to be located somewhere that is representative of the house temperature. From what you've said that wants to be in your living area. If you're going to be turning off the heating upstairs then that's not the place for it, nor is the kitchen, bathroom, workshop, porch or outside! Keep it away from your woodburner and radiators.

Just reread what you asked and realised that you're talking about the HW temp in your HW tank?? In that case the answer is no. The heat pump runs at different temperatures when it's heating the HW tank and when it's heating the radiators. The change in temperature is done automatically but you can set the time and temperature for both the HW and central heating.

Yes it does...the hotter a radiator is the more heat it gives off. The hotter you run the water leaving the heat pump the less efficient it becomes so it uses more electricity and costs you more to run. The solution to this problem is to run the heat pump cooler and have bigger radiators.

Any excess PV goes to power your neighbours and likely reduces their fossil fuel demand so a lot more to use surplus PV for other than generating export income. A definite meaningful use for it especially if it's tax payer funded via grants/subsidies

Unless you've got a sizeable solar array and batteries, solar wont generate much electric in the winter when you need the electric the most to run the heat pump. You're probably better spending your money on sorting out the heating system you've already got to get the lowest running cost you can. Once you've done that you can choose how much or little you heat the place.