Dreadnaught

@Dan F, I see that the controls on the VRC720 allows for a given Zone to be controlled by a remote control. Could it be possible to connect your slab thermistor to a remote control in some way and then link it to a zone. That way the controller could target a slab temperature for the ASHP rather than a room temperature and so give you finer control. No use of exotic ebus commands required. Just an idea. @Dan F, with your background in software & technology, I suspect you're more ingenious than I.

Makes sense. Thank you. Sounds like it may be wise to constrain the cooling with a higher minimum temperature and perhaps a shorter cooling window. Not ideal, short of directing the controller to watch a sensor embedded within the slab (or the temperature of the return water in the UFH pipes).

I am following this discussion with great interest. I haven't bought my ASHP yet but was planning to use exactly the same setup as you @Dan F, including with a passive slab. I have had a play with the VRC720 online simulator and read the manual. For controlling the cooling, there seems to be a number of controls available. Do they not meet your needs? It is unclear to me if the cooling circuit uses weather compensation or if that is limited only to heating. If not, then how is the water temperature set in cooling mode? @m0deller, in MENU → SETTINGS → Installer level → Installation configuration → Installation → Automatic cooling. Have you turned this on to automatic and set the two temp setting appropriately? See below.

Hi @Simon R, great post. Thanks for posting. A splendid to hear @Jeremy Harris being mentioned. You mentioned the site "wood online". I tried Googling it but came up blank. Do you have a URL for it?

Interesting discussion. Playing devils advocate, @PeterW, the reason you might buy a spool of cable and terminate it oneself is because Cable Money only sell a range of lengths (3, 5, 10, 20m, etc.) and, with decent gear, terminating is actually quite easy. What say you? (This is relevant for me is I will be running my ethernet network soon-ish in my new build.)

Slightly off topic but somewhat related is the matter of the reclamation of VAT under the government's "VAT DIY Scheme". If the property is deemed by HMRC to be being built for profit, I believe that the ability to reclaim VAT under the above scheme is also lost.

One subtle point of difference, @puntloos, for you to consider (and maybe ask MHRC about if you are calling them). I am under the impression that the 2-years mentioned is just a useful rule-of-thumb. The real underlying principle is whether the new property being built to make a profit or not. The 2-year figure is a time interval that can often demonstrate that, at the time of building the property, there wasn't an intention to sell it to make a profit. However it is the underlying principle that matters and not the time interval as such. Two examples that illustrates the point. 1) A self builder builds a house for themselves without any intention to sell. Life changes, such as a change in job location, mean that they sell it the moment it is finished and move with their job while making a profit. I think that it would probably be easy to convince HMRC that this was their PPR with no CGT to pay. 2) A self builder builds a house, lives in it for two years and sells it for a profit. They tell HMRC that its their PPR so no CGT to pay. Self builder then does the same thing subsequently three times in a row. Would HMRC then make the case that the self builder is actually a developer building houses for profit. I think they might. Would back taxes become liable, I don't know.

Yes, I see what you mean. Perhaps they are the same item, and with that part number it is for Vaillant's gas boilers. Or perhaps they used the wrong stock photo on the internet page. At just £5 it could certainly be worth a try!

Hey @Dan F, you could get your multimeter out and test the resistance of your one for us. You could sell the information to each of us for £250 a head and we'd all still make a profit after we've spent less than a £1 on materials 😄 (Joking).

Those light fittings looks splendid. Dimmable too. I see some have drivers built-in but others require an external driver. I am interesting in a driver that can be connected to HomeKit. I wonder if they can be driven by, for example, IKEA's LED TRADFRI driver. https://www.ikea.com/gb/en/p/tradfri-driver-for-wireless-control-grey-60342656/

Thanks @john0wingnut, I hadn't heard of NIBE. Had a quick look. I see they do a 6kW model using R410A. Is that the model you have?

Thanks Dan. Speaking to Midsummer about paying £300 for a resistor that costs pennies, they initially suggested an R32 Samsung unit instead, which has cooling enabled straight from the box. But Samsung's equivalent of the UnitTower (called Climatehub (!) is pricier so all-in-all there was not much saving to be had. And the Samsung heat pump is noisier too. Given the saving on the resistor I checked heima24 for the price of the Arotherm Plus itself and UniTower. I would have no qualms about importing it from Germany rather than locally within rip-off-Britain. To my surprise, the German list price was rather more than my UK quotes.

Good point. Here's an example from Belgium: https://lbge.be/product/vaillant-codeerstekker-voor-activatie-van-de-koelfunctie-0020269259/, €51

From the "£300" quote was from the wholesaler, Midsummer Wholesale in this case. The only seller I found was this one, £391.20 inc. VAT. https://www.heatingandbathrooms.com/coding-plug-cooling-function If only we could find the Ω-rating, I bet you could buy one for pennies and solder it oneself.

About the cooling resistor for the Vaillant Arotherm ASHP … I just contacted the company who will supply the ASHP and they said "Yes you need a coding resistor for cooling function. It's pretty pricey. About £300 from memory." Anybody know of a cheaper solution? Or did anyone buy it with the resistor already fitted? This video shows the resistor fitting, which, other than the protracted checking-for-a-gas-leak, seem to take about 2 seconds.