ProDave

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.

The official flood risk map shows a very high risk of surface flooding immediately to the south of our plot. Correct. In very heavy prolonged rain, the water table rises to the point the field floods. But it is no risk to us as the flooded part of the field runs off into the burn, and the ground level on our side of the burn is higher. It's things like the local topology that matter, so if your house is even slightly higher than the surrounding land, any flooding will just run off somewhere else. I guess your biggest risk is if the pumping station failed and the industrial scale water extraction stopped.

I am happy with our static caravan now serving as a shed / storage space / additional work space. Nobody is ever going to accuse a static 'van of being "well insulated" but condensation or stored stuff going mouldy or getting damp is not an issue. They are probably easier to buy and install than a container.

Can you show a picture of a pair of joists fixed together with these brackets? I am struggling to understand exactly what they do?

Yes move that to the pump terminals. It's as if the installer did not have, or could not read the very clear wiring instructions. Or simply did not understand them. Sadly I have found several UFH installs where the installer did not have a clue how to connect them properly.

Yes. A screen grab of the important bit The red and blue wires shown here going to the boiler are a volt free normally open contact that does exactly what your relay is doing, closes when the UFH pump is on. Ditch your relay and connect the Red and Blue shown here to the EVU

Quite apart from the probable drain problems you will encounter, is this extension really worthwhile? At 1.7 metre wide externally that will be about 1.4 metres internal width. Not a lot at all. So it will be an expensive extension for not a lot of space, and in building it you block access to the garage and lose a parking space. I suspect that will devalue your house, it would certainly put me off buying it.

Looking at your diagram, the wiring centre IS providing Switched L and N to the pump. and A1 and A2 on the relay is the relay coil. So the relay turns on when the pump is running. 3 and 4 are a normally open contact on the relay. So the relay is NOT switching the pump, it is providing a volt free open / close contact to the EVU This relay should not be necessary as most UFH controllers will already provide a volt free contact of some sort often labelled as boiler or call for heat, which will provide this volt free contact without needing the relay. Can you post a manual or a close up picture of the connections available for your UFH controller?

Most people don't have any form of relay in their fuse box to turn the heating on or off. So can we get to the bottom of why you have one, and what generates the trigger signal to turn it on or off? And how often does it turn on and off? A SSR probably could technically be used but the question remains why? Not something most heating systems need.

Our first build we did that, completed the house before the garage. No issue with planning, but building control required us to do the building warrant for just the house so they could issue completion on that and we could do the VAT claim, and then a separate building control for the garage. Of course it meant the materials for the garage you could not reclaim the VAT.

You MUST keep moving. You cannot store fitness. It will go away very quickly of you stop doing things. In the "off season" we try and go for a good long walk a few times a week to keep things moving.

Tell the council you expect the end wall of the replacement balcony to be opaque to prevent overlooking of your garden.