Jeremy Harris

There's always the option to buy the land then gift it. No problem with that, AFAICS - inheritance tax liability for 7 years doesn't work backwards, does it?

The current rating depends on how the cable's installed, and yours will end up being under EWI, so needs to be de-rated. TLC have a cable size/voltage drop calculator here: https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html that's a good general guide, but there needs to be a de-rating factor applied if the cable is installed in a way other than clipped direct or buried.

Might be worth playing very safe and fitting a battery powered dry contact thermostat, as that way you know there are no high voltages around, although a relay would be fine, if you can find a neat way to mount it.

Our 7 kW ASHP is nominally 20 l/min, and looking at the data for the others in the range, the 12 kW model is 35 l/min and the 14 kW model is 41.7 l/min.

IIRC, wasn't that Wunda not knowing anything about a product they were selling? The thing that gets me with them denying what they told you on the phone, is that their plain wrong technical advice could have killed you, rather than just blown the ASHP main board. They told you that the contacts were isolated and that the case of the product had been marked wrongly, so you might have taken them at their word, handled the wiring from the supposedly isolated contacts and been electrocuted because they weren't isolated at all. I bet a court would have taken the advice they gave, and which you relayed here, into account if such a dreadful thing had happened. I think the clear message is to not trust anything they say in future, as trusting their advice might just kill someone.

Well, seeing as there is an audit trail as to what you did here, in this thread, I think Wunda are bang out of order. Certainly not a company I'd do business with again, that's for sure. I'm tempted to point them at this thread so they can read for themselves about the way they mislead you and caused you to damage the main board of your ASHP. Hopefully others might read this thread and choose not to deal with Wunda, given that their advice and technical data is so bad. Worth noting that they don't have the technical details for that thermostat on their website, either. The installation instructions I dug out and posted earlier came from TPS, not Wunda.

Cable size depends on the length more than anything else, as with a single phase domestic supply you're not going to have a charge point that's larger than 7 kW. The maximum current would be around 30 A, which is OK on 4mm² up to a distance of around 35 metres. I'd be inclined to run SWA in the wall, rather than fit conduit, as if there are any bends it will be a pig to pull a thick cable through once the conduit is behind EWI, You can always just leave excess SWA coiled up, with the outside end sealed up, until such time as you're ready to fit a charge point. A 7 kW charge point will usually have a 40 A double pole protected circuit, so worth looking at whether there's space in your consumer unit for a DP RCBO or whether you'll need an additional small consumer unit to supply the charge point. The Tesla home fast charger needs a 3 phase supply, so would require a new supply to the premises. A 7 kW single phase AC charge point will take around 9 hours to charge a base Model 3 from fully discharged.

I've found an Italian supplier that has it listed, but with no price and a really clunky website: http://cantieriazzurra.com/ECLinkProduct.asp?grigliaOrder=Sorter_product_s_desc&grigliaDir=ASC&product_id=289306&newtitle=Compatibile

I've found the Computherm Q3RF thermostats to work very well, and can confirm that they definitely have dry contacts on the receivers, so are safe to use with a low voltage DC control system. If you want a programmable thermostat, then the Computherm Q7RF looks pretty good. The main reason I chose the Computherm stats was that they have the option of changing the switching hysteresis to +/- 0.1 deg C, which helps to reduce temperature overshoot in our application. Computherm Q3RF.pdf

From your description there's no data coming from the ASHP, but the unregulated 12 V supply is OK, as that's what powers the command unit. There are several sensors in the ASHP that all send data via the serial data link to the command unit, on request, including the external temperature and humidity. The room temperature sensor is inside the command unit, so not reliant on the data link to the ASHP main board. A quick additional check as to whether there is communication between the command unit and the ASHP main board would be to try and look at some of the sensor data using the diagnostic function in the command unit. My money is on there being no data communication, which would almost certainly mean that the main board has suffered a fairly catastrophic failure. Worth trying the diagnostic menu, though, to be sure. Look for an E3 error code on the command unit, as this indicates communication failure, and is displayed briefly in the external temperature display before that just goes blank.

From the lack of external data being displayed on the command unit, and the fact that the command unit is still working, we can deduce that the 12 V supply is OK, as it runs the command unit (there's a 4 wire power and data cable between the command unit and the ASHP main board) and that data is not being transmitted by the ASHP to the command unit, as the external temperature and humidity isn't being displayed. The serial data link is RS485-like, although it seems to use a proprietary data format. I did have a go at sniffing the data to try and see if there was a way to programme the ASHP non-volatile memory without using a command unit, as one or two here have bought units where the command unit wasn't supplied (including @joe90, I believe). Kingspan seemed to sell these units without the command unit, whereas Glowworm sold them with. Not sure about the other badged versions of the same unit. Once programmed, the ASHP does run perfectly well without the command unit, but there's then no way to change things like the weather compensation curve or any other temperature set points. The command unit can be used as a programmable thermostat, as well as just a programming interface, so can replace the default dry contact switching system these ASHPs use. The only downside of that it that the command unit human interface is a bit clunky, IMO, and not at all intuitive to use as a programmable thermostat.

Just realised they are in the Netherlands, rather than France, even though they give a contact in France it's a Netherlands country code on the number.

I'd be telling Wunda to pay up too! I can only find one supplier listing that board, no price and they are in the Netherlands: https://www.smith-europe.eu/en/sales/marine-refrigeration-parts-list/carrier-marine-parts-14/ There's a long list on that page, but the board part number is listed a long way down; search the page for B036601H03

The command unit is powered from the low voltage supply on the ASHP main board, so it looks like the power is there. The outdoor temperature and humidity data is processed by the main board in the ASHP and transmitted via a serial data link to the command unit, so it looks very much as if the data handling and control side of the main board has failed, rather than the power supply. I suspect a new main board will be needed, but at least you have the command unit, so can programme it with the settings you need, even if it's just to download all the default settings into non-volatile memory on a new board. It may be that a new main board comes with all the defaults programmed, but it's possible that, like a boiler main board, it doesn't, and needs to be initially programmed by connecting the command unit. A new main board seems to be around £100, from that other post; maybe you should try and get Wunda to stump up for it, as they told you that the thermostat had dry contacts when it didn't.

Both contacts need to be linked to get it to turn on and provide heat - link 0 V (terminal 3) to both terminals 6 and 7 and the ASHP should just turn on and run.

I hope it's not done any damage, too. With luck the 12 V connections in the ASHP have some form of protection. If there is damage, and as Wunda told you that the thermostat had dry contacts, I wonder if you could claim against them?

I've managed to find some more info on the thermostat you have, and it seems there are three variants. I've attached the pdf to this, but you may already have it. The part numbers vary for each model: E91.713 and E91.716 are mains output units (not isolated) with the first being the 3 A version and the second being the 16 A version. They have markings that look identical to those on your unit. E91.723 is the version with potential-free contacts on terminals 4 and 5, and looks different to the unit you have. E9_manual.pdf

I have an outdated copy of ours on our blog, here: http://www.mayfly.eu/wp-content/uploads/2016/12/Simplified-costing-spreadsheet-050421014.pdf Bear in mind that it's four years old, plus I failed to keep it updated with the final costs...

The heat pump is tripping out because there is a flow restriction, I expect. Mine did the same until I fitted a bypass to allow the flow and return to be "short circuited" in the event of a valve not opening in time. Look at the error code on the command unit - I bet your seeing fault code 9, which is triggered when there isn't enough flow through the unit. The cause of this for my installation (where the heat pump has an internal circulation pump) was because the valves allowing flow to the UFH and buffer were too slow to open. As a result the ASHP sensed insufficient flow and shut down, then tried to restart around 30 seconds later. If left long enough it would fire up OK, after the UFH thermally actuated valve had opened (takes a few minutes). Fitting an adjustable pressure bypass valve fixed it, as that now opens if there is a closed valve and allows water to circulate around the flow and return, keeping the heat pump happy.

Heat pumps are best suited to a relatively low heat loss house, for a couple of reasons. Firstly, the size of the heat pump needed is set by the worst case demand, often the heating demand in very cold weather for a house built to a relatively poor standard in terms of heat loss rate. That then means the heat pump will probably be quite large and so more costly, usually. Heat pumps don't like delivering water at more than about 50 deg C, even a GSHP will lose efficiency when the flow temperature gets this high. Heat pumps generally work more efficiently if the flow temperature is reduced to around 40 deg C or less. An older house may well need water fed to conventional radiators at a higher temperature than this in cold weather, so would need either retrofitting with UFH (if practicable, as there's a limit on how much heat UFH can deliver) or have the existing radiators replaced with larger ones. Hot water is another potential problem area, especially if an existing house only has a small hot water tank, run at a high temperature. With the upper limit for most heat pumps being around 50 deg C, the house may need a larger hot water tank in order to be able to deliver the same quantity of usable hot water at the taps. You only need water at around 40 to 45 deg C at the hot water tap, but often hot water tanks will be run at around 60 to 70 deg C and the water at the tap will be mixed down with cold to give a comfortable temperature, which then allows a smaller hot water tank to be fitted, as less hot water is drawn from it due to the much higher temperature. If there is a mains gas supply available, then generally it's cheaper, both in terms of initial cost and running cost, to fit a decent condensing gas boiler than it is to fit a heat pump. If there isn't mains gas available then the chances are that a heat pump, with modifications to the radiators and perhaps the hot water tank, may prove cost effective, because of the reduced running cost over its lifetime. This may be marginal though, for a house with a high heating demand; you probably need to work through the actual data for a specific house in detail to see if it would make sense.

The cells in the old Sunamp PV were removable, and a lot smaller. There were photos of the assembly of those at Sunamp, on their old website, I think, that showed filled cells in a row, waiting to be fitted into units. The Sunamp PV I had (well, technically still have, as it's waiting for me to move it downstairs so it can be collected) had two much smaller cells in the lower part of the enclosure, with a circulating pump, heating element a couple of non-return valves, an ultrasonic flow sensor and the control electronics in the upper part of the unit. The case of that was more complex and bolted together in sections, so it was relatively easy to take the cells out. The Sunamp UniQ 9 we now have is much larger and almost the entire volume of the case is filled with a single large cell, with vacuum insulation panels around it. There's no pump, valves, electronics etc inside the case any more, instead the heating element is in the base of the cell and heats the PCM directly. There is a separate control box that houses the electronics, and senses the state of charge of the cell by a vertical chain of thermistors inside the cell. The control system seems simpler than on the Sunamp PV, in that the relay that connects the heating element to the incoming power (either diverted excess PV or a directly connected supply) is activated whenever the cell charge drops below a set level (either 50% discharged or 90% discharged, it can be set on the control unit). The Sunamp PV used to switch on and off depending on whether there was any power coming from the PV diverter, whereas the UniQ just connects the heating element to the incoming supply whenever the state of charge drops below the threshold, and allows the PV diverter to do the switching. The other function seems to be that the unit now has a start from cold mode, where if the PCM is completely solid (so fully discharged) it pulses power to the heater initially, presumably because if it didn't there would be a risk of locally overheating the PCM immediately around the heater. As soon as the lower part of the PCM has turned to liquid, the control unit switches out of cold start mode and allows full power to be fed to the heating element. All told it's a great deal simpler than the old Sunamp PV, with none of the complexity of pumps, valves, flow sensor or whatever. It's pretty much like a conventional thermal store, with a pair of heat exchangers inside the PCM to provide "instant" water heating and an electric heating element at the base, rather like an immersion heater. The unit I have is roughly equivalent to a 210 litre hot water cylinder, but a great deal smaller and with much lower heat losses.

The DNO issue goes back a decade or so to the time before we had inverter controlled heat pumps, when they were unmodulated, "on-off" machines, with a conventional direct online starter. The starting current could be two or three times the running current, and it was this that caused the DNOs concern, especially as most early heat pumps were quite high output units, so tended to have a pretty high input current to start with. The 7 kW unit we have draws a maximum current at full output of 10 A, and most of the time ours runs at around 2 A. There's no startup surge, as the inverter starts the pump and fan slowly, so the current remains under 10 A at all times. An electric shower rated at 10 kW at 230 VAC draws a bit over 43 A.

You need to work out the heating and hot water requirement to see whether it's worth going for an approved installation so that you can claim RHI. When I did this, the cost of an ASHP that was smaller than the one we have now, supplied and fitted by an approved installer, was around £4,500, IIRC. The RHI payments would have been £84 a year for 7 years, so a total of £588. I paid £1,700 for our ASHP, installed it myself (very easy) and so paid probably under £2,000 for the whole installation. I don't care about the RHI, because even allowing for that with an approved installation I still saved close to £2,000. It made it daft to think of using an approved installation, as I'd never have got the additional installation cost back.

We were going to use a second borehole, as we already had to have one for water, so the extra cost of drilling a second one for a heat pump collector was relatively small, as a big hunk of the borehole cost is in mobilising equipment to the site and setting up.

All the weight is in the cell, too, so there wouldn't be much to gain if you could get it out. Also, I don't think you can get a cell out of the newer units - it looks like it's filled with PCM via the pressure relief valve after the cell has been fitted into the case to me.