ProDave

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.

There will likely be an inspection chamber in the front garden where it changes direction. Lift the lid on that and you should be able to find out exactly where it is and how deep, and the exact direction it runs, those plans are not always entirely accurate.

Can you show a picture of the ends where it splits and where it goes into the consumer unit, and a picture of the consumer unit with the lid off if you are happy doing that. Is there just ONE cable or a pair of near identical cables?

Ridge tiles off and more lead flashing done properly. Whoever put that little square bit at the top is NOT a roofer.

That is common for old stone houses here, and you will note from the pictures the studwork is pegged to the stone wall in several places.

Ha Ha. I had that "discussion" with Scottish Water. THEIR meter box has a SINGLE check valve. My own boundary box that followed it has a SINGLE check valve. NEITHER are any good, not even both of them together. They would not connect me until they could see an additional in line DOUBLE check valve. Makes you wonder why they supply and fit something that is not fit for their own requirements.

The very left hand item in your diagram is an isolating valve and double check valve (non return valve) that will stop back flow. That is a requirement for any new house now. with or without accumulator or anything else.

A heat only aka system boiler gets it's call for heat usually from a wiring centre and one or more motorised valves and a programmer. There will usually be a cylinder thermostat and a programmer and possibly a room thermostat somewhere as well. A smart thermostat would go in place of or as well as the standard programmer usually. Whoever connects the smart thermostat needs to understand what controls are there and how to connect it to work with those.

And tomorrows Agile prices up to £1 per kWh for even longer than today.

It could also be a problem with the fan motor? Most heat pumps use a fan motor with a built in speed controller, and they have a fan rotation sensor output. If the fan is failing to run when set to high speed, it would not give the fan run signal and the heat pump would not start. but you would expect it to give an error message to say that is the reason.

You don't want it too hot under the floor. If the UFH temperature is lower that means it draws hot water out of your local calorifier more slowly, so should not affect the cost to you.

Ah so you buy hot water from a central source? that is usually fed into a local calorifier in your property and metered at that point. The temperature you mix it down to for your UFH would make no difference to the cost you are charged.

Can you post a picture of the Carel controller? Our village hall has a Dimplex Ground source heat pump. When the Carel controller for that packed up, it was £1500 for a replacement and then a lot of hassle getting it to work as there was very little information and in spite of being told it was configured correctly for our heat pump, it was not. I doubt yours has the same controller but I am interested to see what is there. Try and get a range og photos, close out showing the whole lot and close in showing the terminals etc.

Of course we are, and I can see storage smoothing out the peaks and troughs as demand changes throughout the day. But these winter anticyclones are not unusual, and can typically last 1 to 2 weeks. That is going to be a LOT of storage to last a week. Or make the price so high everyone turns their lights and heat pumps off and shivers in the dark......... In front of the backup WBS. This is why I just cannot see an electricity grid working without some other input, even gas power stations mothballed on care an maintenance ready to be fired up in such weather conditions.

This is what worries me about the future, when even more of our energy comes from wind, and a winter high pressure means not enough wind. And imagine a day when we are all forced to have a smart meter and forced to be on a variable tariff? EDIT: If I check tomorrows prices for my own region, Northern Scotland, it will be over £1 per kWh tomorrow afternoon. Kind of ironic the region with most of the windmills would pay the most.

OUCH. I guess that's because of the high pressure and lack of wind? Which is NOT unusual in winter.