ProDave

So the ASHP is consuming 1.6kW to heat the house, assuming a COP of 3, that will translate to 4.8kW of heat delivered to the house. It is very cold at the moment. Our very well insulated 150 square metre house needs about 1.5kW of heat at the present sub zero average outside temperature. So your house is larger, older and no doubt less well insulated, so 4.8kW of heat does not seem at all unreasonable. Don't expect to reduce that significantly other than as above move to a smaller much better insulated house. What exactly does that mean? surely not the heat pump is set to heat water to 88 degrees? Sounds very like it does not have the right sort of hot water tank for a heat pump. Not much you cn do there as the system is not your to make alterations to. It sounds like your expectations of the property are not matching reality, and as above again, all you can do is move to a better property.

If you still have the old type of ball cock valve that shuts off the water slowly and can take ages dribbling to fill the last little bit before shutting it off, then change if for a modern fill valve, that will fill at full flow until quickly shutting off when full. You will never again want to go back to the old slow ballcocks.

So that is not a rainwater pipe, but outflow from a bathroom? Bodgit and scarper plumbers strike again. Replace that downpipe with the proper round downpipe that will mate with the other black pipes all the way down.

Cuddle Puddle

They may be a reputable company for complete light fittings, but I have not found spares on sale anywhere yet. Perhaps try contacting Siteco directly and asking them if they can supply you with a new driver?

Most likely to be the driver. Trouble is I can't find that exact driver anywhere. The important thing is you want a constant current driver set at 145mA or an adjustable one that can be set to that. Most I have found are 300mA or more. Then it has to be small enough to fit in the space occupied by that one. If it were mine, I would open up the case of that driver which may involve cutting it open of the plastic is welded or glued shut. Like @Temp my money is on a failed capacitor or 2 which is probably repairable. Even if you then had to glue the case of the driver back together. P.S the U Out 340V DC makes one not trust much of what is written on it.

Can you post a closer picture of the Sireco module. Even if I zoom in, it is too fuzzy to read the numbers.

That looks like a 1W switch (simple on /off) A 2 way switch would have another terminal in that hole circled in red. For the few p you save I only buy 2 way switches

How much did you use in your house? No more than 500M in mine, if that, and by buying new offcuts you can get it pretty cheap. e.g 90 metre "offcut" for £60 with postage https://www.ebay.co.uk/itm/316187121886? 5 of those would have done my entire house. At that price, just put it in, it gets used, or if not, you have not wasted much.

I used to build industrial control systems and there is a defined risk assessment that considers likelihood of a failure and consequence of a failure to determine what sort of control system was required. For most of what we did (machines that could kill if the safety systems failed) that was 2 contactors in series, with a safety relay monitoring the state of the contactors and would not allow the machine to start if it detected one of them had a stuck contact. Now given a boiling unvented cylinder could explode and kill someone if the safety systems failed, I would not want to be the one standing up in court explaining how I designed my own 24V contactor driven "safety" controls rather than using industry practice as described in the installation manual. I did encounter an ASHP installed to it's manufacturers instructions (I forget which make / model) and that connected to the immersion heater in the UVC WITHOUT a thermostat on the immersion heater itself. I was most uncomfortable with that, but I neither installed it or altered it, just observed what was fitted.

I am not familliar with the heating system you propose. Is it warm air heating delivered by the MVHR? If so previous discussions suggest to deliver enough heat it will have to run at much faster flow rates than normal mvhr. I would put those UFH pipes in and go that way. You will almost certainly only need that on the ground floor as we have. What do the heat loss calculations say is the heat input needed on the coldest winter day you can expect?

Does your heat pump expect to connect to the immersion heater? If so that dictates a lot of the controls and you have to work or adapt around that. In my case the ASHP does connect to the immersion heater (though I have disabled all use of that in the settings) and it does so with a control box supplied with the heat pump, which contains a contactor and mcb's. To integrate that with my PV dump controller, I modified the supplied box to single pole switching, so only switching immersion L via the contactor, and then connected a solid state relay in parallel with the (now single pole) immersion contactor switched from my dump controller. The use of a remote SSR for the dump controller was a big motivation for making my own. The immersion heater will have it's own normal thermostat and secondary over heat protection should that one fail. The cylinder mounted thermostat with a probe in a cylinder pocket is to protect the cylinder from over heating when fed from an external heat source, so should be wired to close the motorised valve on the cylinder input coil if the cylinder is overheating.

Okay 1 more. First self build, over 20 years ago now. Originally planned a square shower tray. UFH pipes laid out to suit that. Floor marked with big marker pen showing where every single pipe was. Changed plans. Decided on rectangular shower. Waste in a different place. Cutting the hole for the waste, a fountain of water started to come from under the floor. Yep I had failed to see my own markings and cut right through an UFH pipe.

Neither. For simple white switches, I don't think you will beat Click Mode for quality, value and reliability. But Screweys don't sell them. Toolstation do. https://www.toolstation.com/click-mode-10a-switch/p73508 A little "quirk" of these switches is the switch mechanism can be removed from the plate, enabling you to mix normal and intermediate switches on the one plate. Almost like a grid switch.

As above , if it is just a workshop / shed (i.e. you don't intend to fit a car in it) I would be very tempted to have two buildings within the size limits for permitted development and not requiring building regs. Given the aparent L shaped nature of the garden from your plan, I would personally tuck the building(s) just around the corner to the right so not obstructing the straight run of garden from the house.