ProDave

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?