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You can get a range of contactors typically with 240VAC, 12VDC or 24VDC coil voltage. They all draw ballpark 1W to keep the contactor closed to the load on the control relay is ~40mA in the case of 24DVC, doubled for 12VDC, and a tenth of that for mains. I prefer using DC simply because all of the control stuff is low voltage which makes it easier to get signed off.

It's good in principle, however by using a contactor you bypass that function - it will only tell how how much power the contactor itself is using, not how much power is passing through the contactor...

Thank you, I do appreciate I am making this more complex than it needs to be. Part of the need for 'smart' control is that the setup is in the loft and I can't run any more cables. I would like to easily adjust away/holiday settings. @JohnMo sorry what does this mean? "Hot water sorted mice on with your life. Change from £30" I am now leaning towards simple timer switch for hotwater tank. Our water usage is 2 showers morning, 1 shower and bath(3 young kids) evening. Buffer supplies ufh only and in recent cold spell the flow temp of 37drgrees was sufficient (and still some more insulation and airtight work to do, loft hatches to close etc...) trying to run it as low as possible. I would definitely want on a smartish system for the buffer, Minimum remote control, love Shelly's power monitoring. @Mike thanks for that diagram, very helpful

My point is "chasing net zero" isnt (in the main)" to our detriment. The whole crux of the anti net zero argument is that it somehow is worse than the alternative, that is carrying on burning FF as our main energy source and not moving to a more advanced technological system. If we stay"as is" or worse yet go backwards we will be shooting ourselves on the foot whilst China and the developing works eat our lunch. China already has a massive lead on us. PV is the cheapest electricity source available, especially towards the equator. African countries have worked this out and are jumping straight to electrification. We are going to have to face economies with lower energy costs than us because they are either in renewables or have vast quantities of their own fossil fuels (or ones from countries they invaded) The countries at the bottom of the heap will be the idiots who have set their e onomy to rely highly on imported energy

You paid your electricity bill and taxes right? There you go. You paid for the coal fired power stations. (well actually taxpayers pre 1980's did as the big coal stations were built under nationalised industry. - private generators only came after the 90's.)

If you have issues just email them, they are super helpful. It's worth using a CT clamp on the diverter valve power feed, then the data is split for heating and DHW. Also unable auto cooling detection while you through the settings.

We don't need the immersion to clear the legionnaires risk the heat pump does that. So for now I have wired it straight to the CU breaker via a switch fused unit. So as of now we don't have automation of the immersion but there appears to be nothing preventing me using my contactor approach. The rules are clear that you can put stuff in between those fixed points provided it meets the wiring regs etc which is how the diverters do it. So I won't have any high current stuff on / around the tank other than the connection from Switch Fused Isolator to the immersion heater. Final job is to commission the heat meter & EmonPi. Hopefully Sunday, then I will have some real data to play around with and get an impression for how good or bad the system is.

I'm not sure what you mean. We, and much of the west, exported our manufacturing (and energy/fossil fuel consumption) to China. I posted the chart to show that we're chasing net zero to our detriment while China forges ahead. What's misleading about that?

It's funny how the cost of new energy infrastructure is added to energy bills like that. I don't recall in days gone by paying a levy to pay for all the coal fired power stations?

In fact, there are subsidies paid to the "community". It turns out our local community council receives payments from at least one of the nearby wind farms. I don't know of the history if how or why these are paid. The money is supposed to be used for the community good. One of the things they spend it on is a modest annual payment to each household to help with energy bills, with a higher amount paid if you are over state pension age.

£xx on every electrical bill for ever more

I just use a Sangamo PSS2 time switch. Paid £17 for it. Connected direct to CU dedicated fused outlet, then 2.5mm² cable, to an isolator switch near the cylinder, then direct to immersion - all standard stuff, any electrician can fix, any day of the week, with bits from local electrical factors.

I didn't say they could build cheaply, I said more cheaply and quickly than the UK. How much are the two most recent UK nuclear plants costing? £40 billion each by the time they're finished?

As @JohnMo says, if you can use a time switch that's the easy and cheap option. For the Shelly solutions, the main practical difference between the Pro 1PM and the 4PM is that you need 1 x 1PM for each device (heater, in your case) that you want to control. The 4PM can control 4 devices (and has manual controls in addition to smart controls) and would work out cheaper. Here's a diagram (modified from my installation to cut out some bits) that shows the wiring; your electrician may prefer to use RCBOs instead of the breakers & RCCB shown here. The latest version of the 4PM has a single live supply terminal, not 4. I'll be wiring the snubbers directly across the contactor terminals, as shown. The one Shelly sells has bare leads, which would need covering in heat shrink sleeving for safety. I don't know the T-Smart, but if it only works over WiFi and by using their proprietary app, then it wouldn't be my choice - that's all their brochure mentions.

What was the upshot in the end re the over-temp stat on the cylinder?

I quite agree a ma@ive 122kv pylon in a garden is unacceptable. But are they doing that? Is someone proposing planting an actual 100ft multi phase 120kv transmission pylon (as opposed to a wooden pole) in your garden? And the lines could be underground but A) underground is roughly 4-5x the cost of overhead. B) underground is much more disruptive to install as you have to (effectively) dig a continuous trench the entire length of the route - which adds to the cost. Yes, there will be local impacts in places that historically haven't had any. But then, once upon a time, large parts of the Midlands had to accept not only the visual disruption of coal plants in their rolling hills but the impact on air quality - all for power that was sent to rural Wales etc. The power lines running out from the magnox stations stretch our across the rural visas of the Severn Valley to disappear across the cotswolds.

This is the nonsense currently being spouted by Plaid here in wales. Its NEVER going to happen. But, regardless, i dont want a few quid, i dont want a pylon in my garden. Nobody wants a pylon in their garden. Seeing as we are going to spend trillions and bankrupt the country anyway, for the negligible extra cost, they could underground the cables. Then everyone would be happy. But there might be a hit to shareholders, who probably mostly live in the cotswolds!

Finally got the remote control power supply installed yesterday 3 spare outlets now for lamp post and garage up lighters Spot lights in the sleepers turned out well

France certainly can't build them cheaply. Flamanville 3 was due to be completed in 2012 for €3.3 billion. It opened at the end of 2024 and cost €19.1 billion (in French). In Finland, Olkiluoto 3 was expected to open in 2009 for €3 billion, but opened in 2024 for an estimated € 11 billion.

Still think you are making things way more complex than you need. Main water cylinder top immersion, if you are a low water user just use that set the thermostat and a charge window. If you are a heavy user ignore the top immersion and set thermostat on the bottom element and use a simple immersion time switch. Hot water sorted mice on with your life. Change from £30. Buffer immersion - depends what you empty the buffer into, UFH or radiators. But just do simple. You don't need any of this "smart stuff" I doubt very much you really do and doubt it will save a penny over a sensible simple to run system.

Well, it's gone very well. On Wednesday the system was commissioned with no issues so the MCS cert and the G cert will be issued. When I get a bit of time I will write up the whole thing for a blog as its been a very interesting mission but we got there. It was great to see the heat coursing through the slab pipes. I have not calibrated the Camera for emissivity.

Don't know your planned setup but I positioned my valve to one side of the riser / head. Means you can turn the shower on without getting wet.

Thank you guys This really is a great forum. I have to say a fair bit of this is over my head, I do however want to pin down my final plan. To recap I want to have tight and remote control of x3 3kw immersion heaters. 50Amp RCBO at the main CU. 8m straight 10mm 3 core to loft. Aux CU. Option a) x3 of: Shelly Pro 1pm (16amp) , then 16amp RCBO then contactor then to immersion. RC snubber but.not really clear if this goes across the shelly pro? Does it have to be physically very close and how does it sit in a DIN CU? Option b) Shelly pro 4pm (40amp), then 16A RCBO, then contactor... same question re RC snub Option c) forget Shelly, 16A rcbo in aux CU, then immersion heater, and use this for remote control https://www.tsmart.co.uk/ I couldn't get my head round the 24vdc setup yet. Thanks again

I would be very careful deleting, as your warranty will very likely be void. Almost every manufacturer states you must have a strainer of a given mess size. So add the filter to catch all the rubbish, but keep the strainer there just in case and keeps your ASHP warranty.

I am having a saga still ongoing with this crappy company and what we owe or dont owe for the non existent work we didnt need or have. Before I send a strongly worded email can anyone confirm how much roughly it should be for topping up glycol on the ASHP. It was minus 2 and they topped up to about 7.5. I only ask because by all accounts it looks like they are charging us as follows (although i am about to ask them to confirm as I am sure this is not right). Our quote was for £390.41 for 2 expansion tanks to be repalced and glycol. We paid £195.20 leaving a balance to pay of £195.20 for the work quoted. They say they are applying a reduction of £114 to the outstanding balance of £195.20 meaning we have still £81.20 left to pay. This means in total we have paid £195.20 and they want another £81.20. So a total of £276.40!! I suspect they are charging to fix the leak and pumping up the expansion tanks (even though the second engineer said the expansion tanks should have been pumped up at service). They then may also be charging to come back out the following day when the filter was blocked/error message etc even though the second engineer said he checked it when I doubt he did and we never had any issue with this until whatever he did. I am trying not to blame the problems on what was or wasn't done but it seems we ended up with them causing more issues than we had to start with! And get this...they have given a quote to have work done to fix the coil rattle even though we never had an issue with this until second engineer likely upped the pump speed which i suspect was the cause. So, suggestions how to handle this. I certainly will be asking for a breakdown of pricing for work they are charging for.