ProDave

When it has stopped working and you try turning heating and hot water on and off with the slide switches, do you hear the relays in the programmer go click?

What stops working? CH, DHW or both? Are the Hot Water and Heating lights on the programmer still on when it stops? Can you get it working again by turning the heating or hot water off and back on again?

Nobody can diagnose that remotely. What trips? MCB? RCD? RCBO? or post a picture of what trips if you don't know. Next time it trips, switch the two slide switched to OFF before resetting it. then try with just heating on for a few hours, then try just DHW for a few hours and see if you can narrow it down a bit. The clunk from the controller is a relay energising and quite normal.

Do NOT build it into an accessible space. It has to be accessible somehow e.g in a kitchen, on top of a wall unit etc. Or even build it in behind the light switch and run dc to the light strip?

I have always understood tiles and appropriate flashings collect all the water and send it to gutters etc. The membrane is only there underneath to catch a leak if it occurs and catch any condensation that may form under the tile and trip off. But it is good to test how watertight the membrane is before the tiles go on so you know it is a good backup.

Yes the fault is with the oven. Persevere searching for the meaning of those fault codes. Is it still under any form of guarantee?

That's an rcbo so there is no way to find out if it is tripping due to over current or earth leakage. It's 16A it would have to be a very big oven for that not to be enough,

I would not. I would take the door frame out. Build shuttering either side and pour the concrete IN PLACE. When dry, put door frame back.

Have you looked up what those error codes mean? Is it an MCB or RCD that trips? and does it only trip when the oven actually turns on? Have you tried other oven modes, e.g fan oven, conventional oven, grill?

Or if you create shuttering and pour concrete, is is not really a "beam" as it will be fully supported on what is there already and will just fill the gap you want exactly.

I can see a vaulted ceiling could cost more if for instance you decided to have the vaulted ceiling downstairs instead of putting a room upstairs, it would make the whole house bigger, so real cost. but in our case the roof design was to get an unincumbered room in roof space. So vaulted ceiling or not vaulted ceiling was literally where do I put the plasterboard, insignificant and almost impossible to quantify between low and high ceiling.

do you have lots of fixed resistors available? If so I would connect different values one at a time, say 1K, 10K 100K to start with. And note the readings you get on the heat pump for each. From that you can plot the graph of resistance vs temperature and thus determine the slope of the thermistor required and then buy one.

An MCB only has the "switch" not the little test button as well. A consumer unit with just those, should have one or 2 big RCD's at the end of the row with the test button on.

Mine, from BPC, I forget the make. Fixed from below ducts just push in, cut to length after plasterboard fitted and the outlet just pushes on.

See second part of my reply, if it is really open circuit, how come you get a temperature reading with it connected but an error code when you disconnect it? Anyway a thermistor is marked using coloured stripes using the resistor colour code that looks to be therefore green black black gold. So 500 plus the gold, not sure what the gold means in the context of a thermistor?

Don't trust an MFT for that, it might only have a limited resistance range, try an old fashioned simple multi meter on ohms range. Or at least try your MFT with say a 100Kohm ordinary resistor to check it will read that high. If it was really open circuit, your HP would display the error message that it displays when you disconnect it.

So do you have a multimeter to test it?

I would take a hair dryer on an extension lead and warm it up and see if the reading changes. It is just a thermistor so it's resistance will change with temperature. If you have a plain ordinary multi meter disconnect it at the heat pump end and measure the resistance. Then warm it up and see if that resistance changes. If it does then it is not the sensor that is faulty.

It's an rcbo that is tripping, so you don't know if it's tripping on over current or earth leakage. Do you have another socket anywhere, even in a different property, that has rcd and mcb separate, plug it in there and see which one trips. You mention cutting a longer LED strip short. Did you cut it where shown and are you sure it was a clean cut with no whiskas that could short out? I would expect some form of cap to go over the cut once done.

How do you know it is the sensor that is the issue not with wiring connecting it? If you carefully turn that little square black thing over see if there is any writing on the other side to identify it? Do you have a multimeter?

We have vaulted ceilings but only upstairs, which is a little unusual. Downstairs are all flat ceilings but just a little higher than the standard 2400 But upstairs is all room in roof and to avoid lots of truss timber in the way it is all a cut roof hung from ridge beams. That leads on to making it a warm roof with the insulation and air tighness folowing the roof line. Which gives an unincumbered insulated space the shape of a loft which you can do anything with. The largest bedroom has a ceiling going up to the ridge which then accesses a mezanine above the adjacent small bedroom. The master bedroom has a ceiling not quite as high but flattened out to give a little bit of loft storage space above it, and the bathrooms have normal height ceilings, conveniently giving more storage and space for all the mvhr ducts. Long drop ceiling lights and stepladders access them for lamp changing.

When you are able to turn it off, turn off that main switch and pull out the big fuse to the left of it conveniently hidden behind that post and tell us what rating it is. They only come in 40A, 60A, 80A and 100A. I HOPE it is a 40A fuse in there, it should be, 60A would only be okay if as already mentioned you knew how the cable was routed for it's entire length. Voltage drop might also be an issue if it is a long run.

Open BOTH the black levers, one each end of the flexi pipe. Open is with the lever in line with the pipe, they are closed at the moment 90 degrees to the pipe. It does not matter which you open or close first. Losing pressure at the start is normal as it vents any air left in the system, if it persists, then there might be a leak somewhere.

I am still waiting to see how it is fed at the meter end.

It looks to me just like the sewer serving 3 or perhaps 4 houses in total so I suspect it is just a 4" pipe and it may not be very deep. Look for inspection chambers in your neighbours gardens that will at least help you pinpoint the exact location and ask them if you can lift the lid to see the depth. The issue with building over a sewer is you don't want (won't be allowed) to do anything that puts pressure on the sewer If it's shallow and your foundations would be lower than the sewer then perhaps you might be allowed to build closer to it as your foundations would not put pressure on the sewer.