ProDave

And I expect long after £millions have been wasted, the same will be found true of hydrolysing water to make hydrogen to transport and burn, when it is far better just to use the electricity.

Planners generally want the extension to be subservient to the original house, that usually means the front of the extension set back from the house. The best compromise I managed on a previous side extension was the front wall set back 100mm / 1 brick and retained a straight roof line (by larger eaves on the extension)

I had that discussion with the planners. I wanted a static caravan to live in during the build but wanted to retain it as a garden outbuilding after the build. Planners wanted it there on temporary PP to be removed after occupying the house. When I pointed out to the planners on completion day, I could remove it from the site, then immediately replace it and it would be permitted development they removed the "must be removed" clause.

Are those parts really "integrated" as in built into the heat pump, or just supplied as a package and fitted in the normal places?

you would need more than just one changeover switch. In the summer much of what you use could be supplied by off grid PV and battery, but in winter at times little more than the lighting could work from the solar and battery. A lot of appliances e.g almost anything with a time clock, computers etc won't like the brown out each time you change over.

You need to be SURE of the block and beam make up. If it is NOT well insulated then 20mm of insulation with the UFH will NOT be any good. We can't form much of an opinion from the picture as the "blocks" are missing and all that is there is the beams over a presumably cold ventilated void. You need to solve that one before spending any more effort on this, it might not be viable without a LOT of work. You don't fit UFH for "warm feet" the floor temperature will only be a few degrees above room temperature, so barely enough to make a floor feel "warm" You fit it for even temperatures without the hot spots radiators inevitably give you, and not having radiators taking up walls space and limiting your furniture placement.

So the summary of that is it does not happen often, and if it does freeze your house insurance will cover it. They don't cover the long power cut situation. Sorry I don't want to be having the "you know it gets cold why did you not put antifreeze in" argument with my house insurer. Not have the long period without heating while we argue. What's this antifreeze must not be harmful in case it leaks into the drinking water? NO different to any normal boiler that has some form of inhibitor. Is that also potable just in case?

I would like to hear of someone "testing" that. For instance here in the Highlands, -10 is not uncommon, a 2 day power cut so it can't even turn the pump on to circulate water. Would their heat exchanger survive that? or would they pay the warranty claim without question? And no good if this cover is only during a short warranty and there is no come back if if destroys say a 6 year old heat pump.

So if the pergola went from the outer edge of the patio and stopped just before the garage it would be treated as an outbuilding and PD rules would apply then? Max height 3M at highest point.

Are you SURE you are not prone to high water table at times? That would need to be concreted in here, and because of that I would (I did) dig the smallest hole it would just fit into.

If you do that, please come back to tell us what he found.

Yes keep looking that is not it. Have you tried that test, disconnecting one of the right hand switch wires? Any pictures where cables connect into the actual MVHR inside views of their junction boxes?

That bit we are all in the dark about. Trying to follow the wiring, there appear to be 4 cables in total. 3 of them appear quite normal all with neutrals linked in a connector block. Two of them are feed looping in and out in the L Supply terminal. The third being the L out to the bathroom light in the L Load terminal. The 4th cable is the mystery one. I think it is intended to be a volt free boost switch connected to the N supply and N load terminals. Without doing some testing or finding out where all the other ends go it won't be easy to solve. As I already said I suspect it has never worked properly.

I suspect this is switching 2 different live supplies? as aluded to perhaps trying to boost the mvhr when the bathroom light is on Yes try that. If my suspicion is right the bathroom light will work but not the boost function. Let us know the results. If you get nowhere with these simple tests I suggest you get a competent electrician as it sounds like it has been wired in an unconventional way by someone who did not understand what he was doing and failed to find what was wrong and left it with a blown fuse and hope nobody noticed it was not working.

WHAT trips? MCB? RCD? RCBO if you don't know post a picture of what is tripping. Does the 3A fuse also blow each time it "trips" What is the function of that switch show? Is that the bathroom light switch? It looks to be switching two live cables. Try removing one of the right hand cables (and terminate it in a connector block for now) and see if that changes anything?

Just to add, I am not sure what others use, but mine is filled with "Inhibitor / antifreeze" that contains glycol from one of the sheds, but I forget which one. I had exactly the same concerns with an outside oil boiler in a rental property, when there was a power cut in the middle of a very cold spell. On that occasion I did not know what level of frost protection was in the system, but luckily nothing froze or got damaged.

As above the sections sit inside the one they are sitting onto. It was explained to me that was to allow any condensation to run down the inside of the pipe. If they had mated the other way that might end up running out of a joint. Remember single wall flue pipe is NOT sealed joints. Just a tight fit. There should be plenty of draw in the flue that it is not going to leak any smoke. Connection into top of stove sealed with fire cement.

Depressurise system. Drain the missing quantity from a drain point. Top up that missing quantity with pure glycol at the highest point which is one of the pipes on the UVC then re pressurise.

No problem at all. Particularly up here in the north, they can work very well taking more advantage of the low winter sun. You only need MCS if you intend to export and get paid for it.

I will be the odd one out then. I have Glycol in my system. I do NOT want the heating on 24/7 I prefer it off most of the night and prefer it to do most of the work in the day when the PV is likely co be contributing. I do NOT want an anti freeze valve that will dump my water if it gets too cold. Glycol added at the ratio that will protect the system down to -10C Never been a problem.

Is the house 20 years old or more? Trying to guess insulation levels. Indoor system oil boiler will be simplest swap. Does the old one work at all, if so that gives you an idea of the noise, a new one likely being less noisy. I am not a fan of combi boilers myself but others seem happy.

That suggests it is already laid as a wet room, but the fact it is leaking and the tiles are moving suggests somehow it has failed. I doubt there is a fix other than remove the tiles assess what is under them and repair and replace as necessary.

You still have the tundish, followed by a waterless trap.

If the heat loss calculation gives an answer of 3kW then put simply that means you want a 3kW heater turned on all the time to maintain the temperature. If you put less than 3kW into the house it will slowly cool down. If the house is cold and you want to warm in up, you will need to put in more than 3kW The point about water heating mentioned is as follows. Most heat pumps will only heat the building or the hot water, usually done because then you can have different water temperatures for the 2 functions. So in the perhaps 2 hours a day your heat pump is heating the water tank, it won't be putting any heat at all into the house. So for the remainder of the day it would need to put more than 3kW of heat into the house just to get the average over the whole day up to 3kW.

Have you actually requested a new connection from Scottish water yet? It is not your job to tell them where you expect the pipe to run. Get a quote first and then if they propose a distant expensive connection, then start questioning it.