JamesPa

Well that's no good then, how do you expect the heating controls industry to make any money if you exclude all of the irrelevant components that are also most likely to break down? Obviously that comment was slightly tongue in cheek but at the same time it's worth bearing in mind that the controls industry is inevitably motivated by selling controls, not by our comfort or cost effectiveness. IMHO (and experience with my own heating system) we have been somewhat brainwashed into micro control over past years and the transition to heat pumps is exposing the futility of this approach.

Not sure what question you are asking. Normally there is a 3 way diverter valve between DHW and space heating, fitted on the flow. All of the space heating water circuits should connect to this. The return is not valved. No need for temperature control for the circuits, water will flow through them if they are connected! You then balance the various circuits/radiators for same temperature (or desired temp difference) and you can operate on pure WC or WC with a little bit of room influence. The Vaillant controls are all you really need, providing bags of well thought through flexibility for setbacks/set forwards and various ways to use the room temperature as an overlay to a system essentially run on weather compensation.

Live monitor-compressor modulation on the hoai is what you want. The left hand bar on the hpai display when it's not displaying a menu also gives a visual indication. If you want it to go full whack for any length of time you will need provide a load! Open your windows, turn off room influence, remove trv heads, turn any thermostats to max, operate at fixed ft equal to or above the ft at your design oat. House should heat up to 30C or so. Alternatively you may be able to force 100% compressor modulation in the installer test menu.

Hopefully they are! Leave them that way, (better still unscrew the heads which is what I have done with all but 2 of mine); adjust the WC curve down so the house temp is right, balance the zones/loops/radiators, result: efficient system and more comfortable house. If you have any rooms where solar gain can be large, use TRVs as limiters in those rooms only, by setting them a couple of notches above the target temp.

I think you can guess!, and I fear you will guess correctly! Not sure what 7 and 8 refer to here. In my set of schematics from a year ago 7. No modules 8. uniTOWER, Buffer So 7. Not sure if it actually makes a difference though to the settings, it could, it might, but it might not!

Can you tell us about where in time, 1hr 30 mins is a lot to go through. I did see one with a natty heat pump symbol on 'to help plumbers', doubt that affects the electrical characteristics though.

@-rick- you and I cross posted, I added a bit more detail, references and explanation, you may wish to re-read (or, more sensibly, you may not!) And yes I agree that if an RCD is fitted it must be to the right spec. I cant find the additional Vaillant requirements @sharpenerrefers to, the installation document still seems to say what mine said from 12 months ago.. I dont think you are missing anything. The March document you referred to makes it very clear that the regs dont specifically call out heat pumps which sofaik are covered by the same regs as other external plant not specifically called out

Interesting. I guess this is the heat pumps association trying to do the electricians assessment for them, so potentially consistent with the guidance from the IET that I read. Included in the March 2025 document is this: So it clearly says that there are times, according to the March 2025 document, when no RCD protection is required. So far as I can tell (I dont have direct access to the source material) Regulation 522.6.204 concerns concealed cables installed less than 50mm deep outside the prescribed safe zones (the safe zones are essentially horizontally or vertically from any switch or outlet or within 150mm of a corner of any room including the corners where walls meet floor or ceiling. Cables installed outside the safe zone need mechanical protection against nails, screws etc. I suspect that most cables are, in practice, either surface mounted (ie not concealed) or installed in safe zones, or (under floorboards) more than 50mm deep. Certainly that is true in my house. So if this applies to the ASHP circuit, and unless there is a warranty impact or the manufacturers instructions state otherwise, no RCD is required, according to the March 2025 document. Coming back to Vaillant @sharpener, (and @-rick- the issue of manufacturers instructions) the version of the Vaillant installation manual I have from 12 months ago does not specify that RCD protection is required, what it does specify is that if an RCD is required then it must be of a particular type. This seems still to be the case according to the installation manual here but this manual also seems still to specify type B without any specific additional requirements. I do have an interest in this. My trusted electrician fitted the circuit up to the isolator switch with just MCB protection and was adamant (12 months ago) that this was correct. I was and am happy with this decision. Since the cable is visible throughout its length, that is entirely consistent with the document referenced above. The heat pump engineer then connected my Vaillant heat pump up to the isolator switch using a length of armoured cable which is partially hidden (under a kitchen unit) but anyway entirely within the safe zone. From the document above armoured cable wasn't actually necessary, but I'm not complaining! Since at the time (and maybe now) Vaillant did not specify that RCD protection is required, the whole installation appears to be correct at least at the time, and maybe now if Vaillant are still only specifying the type of RCD if one is required. Phew. Of course (in most if not all cases) there is nothing wrong with fitting an RCD even if it is not required. It will provide additional protection.

Can you provide a reference please. Most recent I can find says that RCD protection (or not) for fixed external plant is down to a risk assessment to be carried out by the electrician.

The point @sharpeneris making, quite correctly imho, is that heat pumps and other equipment should protect themselves from anything that the manufacturer deems it's necessary for the equipment to be protected against. Then local electrical regulations should mandate what is deemed necessary to protect the cable and people. That's a logical split. Anything else is equipment manufacturers stepping into the scope of building electrical regulations, which they have absolutely no business doing. Btw RCDs principally protect people (they trip before a person receives enough of a jolt to be killed, at least mostly) mcbs protect cables (they trip before the cable sets fire due to overload).

What the plumber has done with the plastic pipe is just lazy. It's the 'never time to do it right, always time to do it twice mentality'.

Possibly. 1700l/h is a bit low for 12kW (12000/4200/5*3600)=2000l/h. I would describe this as sloppy plumbing. Why is what appears to be the sensocomfort in what appears to be the plant room/garage. This should be in your house so the heat pump knows the OAT and control the heat pump. Its normally wireless so you can put it somewhere convenient. Maybe Ive misinterpreted the photo. I hope you arent using third party controls/thermostats.

This should be located in the shade where the air is free flowing. If the offset is constant it wont matter much, if its not constant it will and should be relocated. Fairly normal. DHW manufacturers assume people want something close to a full tank or at least half a tank and locate sensors accordingly. Putting it at the top would mean that reheat is triggered only when its empty, meaning that there is a period when DHW is unavailable, which the majority of punters will complain about. Just adjust your schedule/hysterisis to get what you are comfortable with

As @sharpener says they are in the schematics. Not much to be done TBH, everything converges on HPAI. 2 wire bus connecting heat pump , HPAI, WiFi transmitter and wireless interface to sensocomfort/outdoor sensor Connection to sensor in tank Connection to Diverter valve Thats it (other than power of course.)

... which exists as a discussion point only because the backward UK heating industry didn't adopt weather compensation for boilers, unlike many of our more enlightened cousins in mainland Europe. As a result our houses are less comfortable and most are consuming 10% more gas than they need to. When will we ever learn?

@markharro This arrangement is BTW exactly the same as any sealed heating system whether ashp, gas or oil. So any plumber can deal with it and every householder with a sealed central heating system (most these days) needs to know about it!

For my money and to answer your questions I agree with the advice from @JohnMo and @Dillsue 1. UFH re rads is a decision for you based on personal preference and disruption. I presume you currently have rads so rads will be less disruptive. UFH ultimately should be cheaper to run and of course takes up no space. It is generally more comfortable than rads, but ASHP (ie low temperature) heating even with rads is substantially more comfortable thyan traditional high temperature heating. If you go with rads try to design for a FT of 45 or less (you will struggle to get much less). 2. If you are going UFH Id do it now not later. Doing it later means you suffer disruption twice for little gain 3. A mix of rads and fancoils or, if house is reasonably open plan, air to air. I had one fancoil fitted (because a rad really wouldn't) when I had my ASHP was installed, and wish I had a few more. With fancoils, UFH you can do light cooling if your house needs it, which you cant with rads. A2A of course does full aircon. 4. (i) It really depends on the house loss. Ultimately it will need a survey but if its currently reasonably warm most of the day (whether or not you actually heat it) you can get a rough idea from oil consumption. Take you annual litres consumption, multiply by 10 to convert to kWh, then by the assumed efficiency (perhaps 75% if its a very old oil boiler) This gives you an estimate of kWh/year needed to keep the house warm.. Divide by 2000 to get an upper estimate of loss, divide by 3000 to get a lower estimate of loss, result in kW. Suggest you do this and post the result for further comments. You should anyway be doing this IMHO to sense check any survey results, which can be wildly inaccurate (my survey was more than double actual loss, and 50% over appears to be not unusual) (ii) If the house is really lossy then A2W ASHP may not be a good choice unless you plan to upgrade insulation. This is NOT because A2W ASHPs cant cope with the loss, they can, but because ASHPs work best when operated 24x7 or thereabouts. In the vast majority of houses that makes sense, even if they are only occupied part time. However in very lossy, low thermal mass houses (ie houses with, essentially, the thermal characteristics of a tent) point and time of use heating makes more sense. A2A isnt a bad match for this! Hope that helps address your original questions.

Doubtless they will but they wont all have been on a course on qualifying prospects. I haven't either but I imagine that its an inexact science.

I doubt it's anything like as good as 4:1, particularly after you take into account the people who back out altogether.

I think its only intended as a first pass to filter out prospects that are unlikely to proceed. There is a real problem so far as I can for anyone quoting for an ASHP namely that, to do a proper quote you need a proper survey, and that's a lengthy business. For a supplier to 'give away' a survey on the off chance that it may turn into a sale is unlikely to be cost effective (although some do), similarly for an individual to pay the fee which is typically £250-300 is a fair commitment, particularly since surveys are non transferrable. Thus both the supplier and the customer need some sort of pre-qualification mechanism whereby they establish that there is a fair chance that the supplier will be selected. The several suppliers I contacted took various approaches to this. One did a full survey FOC, another would barely talk to me at all without first paying a fee. Most did an assessment based on a 30min visit or call and quoted based on that but subject to full survey. I think the HG online form basically does this first stage. I cant currently see a way round this conundrum TBH, other than by establishing independent survey companies who guarantee their results, so that surveys are transferrable. Cant see that happening. Since any decent installer will be able to get a good feel from the EPC (if there is one) and a short visit, I personally think the quote subject to full survey approach is as good as we are going to get, at least until the industry accepts that records of half hourly gas consumption plus a questionnaire to determine heating patterns is a valid measure (or at least a sense check) on loss.

Yes of course I did! Their online heat loss estimate was closer than the two 'professional' surveys I had done, 10.5kW (Heat Geek AI) vs 16kW (2 3hr surveys), actual 7kW, and it makes it clear that the loss estimate may change when they visit Setting this aside because, as you know, I severely doubt any heat loss estimate that has not been 'sense checked' against measurements, I like the concept. The key new thing is that they seem to be offering you the choice between various flow temperatures (=number of rad upgrades vs efficiency) and between swapping out or not swapping out the DHW tank if you have one. I have long argued that installers should do this so that people can make their own informed trade off between the 'ultimate' upgrade for max capital cost and 'just good enough with the option for an easy future enhancement' for minimum initial capital cost. Not everyone has access to infinite capital funds, and sacrificing long term cost for short term capital saving is commonplace. People take out mortgages, lease cars etc costing much more in the end but making the transaction possible. I see no reason why the same concept should not be applied to heating upgrades, rather than installers offering only the Rolls Royce every time (and then, all to often, delivering a Rolls Royce but with a mis-sized engine, the wrong wheels and ugly accessories that weigh the car down and cripple fuel consumption).

You could probably avoid that by water pumping harder! Depends on the head required/available and pipe sizes. Series connection of radiators is used in some countries, sounds like a nightmare from a calculation perspective but of course doable The problem you may have is that as the oat warms up the DT across the rads will reduce so the ft to the ufh will increase, which you don't want. Interested to see what others say/suggest. A mix of rads and ufh seems quite common. Is there any chance they could just run at same ft with high flow thru rads and low flow through ufh thus bringing the outputs closer than they would be if you had roughly same flow through both.

@SimonD Thanks for taking the time to reply and for setting out whats happening in the industry. I should say that I am very satisfied with my heat pump installation, its way more comfortable than my gas boiler (which was <15 years old) ever was, costs less to run (which I wasnt necessarily expecting), is low carbon and can do some light cooling where I have fan radiators. The DHW is also much better, I swapped a vented tank plus two noisy pumps for unvented, and the improvement is material. However I am rather conscious that I start with a degree in physics so have a reasonable chance of understanding the system, did 2 years of learning about the topic and due diligence on suppliers, plotted 2 years worth of half hourly gas data to establish the loss, and was very selective (and fairly prescriptive) with installers on what I wanted. That said I must admit that 2 out of the perhaps 12 installers I contacted did propose the right system at a sensible price without significant prompting from me and indeed positively contributed to the thinking. Still there was a strong filtering out of the chaff. Most consumers wont have the enthusiasm or knowledge to do this! The nay sayers will shout louder, they are directly or indirectly self-interested in doing so. 'Old-time' plumbers don't want to change and some may even be scared, much of the media has adopted an anti-green agenda in support of their masters, boiler manufacturers and manufacturers of smart (but largely irrelevant) controls don't want to go out of business, and the fossil industry is doubtless helping them all in the background. Then of course you have to factor in that many people are generally resistant to change. Even a 5% failure rate will lead to scare stories which will be leapt on and amplified by those in whose interests it is to do so, and if those 5% aren't rectified, then in a sense its fair to do so. This means that the heat pump industry needs to be virtually unimpeachable It is possible to change the narrative, the media seem to have become much less negative about electric cars, presumably because they have realised that the people who buy them generally love them and of course because the EV industry consistently produces good products. Still I was told the other day that mine might explode (which indeed it might, as might a fossil car, or indeed more or less anything that stores 60+kWh of energy in a very small space and gets mangled occasionally in a crash), but this seems to occur less often. Lets hope that the heat pump industry can go the same way so that we can all enjoy better, greener and probably cheaper heating.

Yes but... It took 6 long man days for a diligent contractor to do my retrofit (it was literally 1 man for 6 long days, no lunch break, starting 8.30 and working diligently until 6pm most days, 7 and 9pm on two occasions). The installation comprised an ASHP, cylinder and 4 radiator swaps. In addition I spent about 1.5days doing prep and make-good for the route of the primaries, and miscellaneous other works, and an electrician a couple of hours wiring in the feed (first fix by me). So the best part of 8 man days in total. If you have the time and appetite for this type of work there is no doubt that you can do it yourself quite cheaply, but if you don't (or don't have the skills), you rely on the industry. The vast majority of the public have neither the time nor the skills which is where MCS is supposed to help. That said when it comes to replacing the unit in hopefully 15 or 20 years time, that seems to me like an easy and relatively quick DiY job.

Based on my experience with installers, exactly that, and they do it rather well. However the point of the system is not to help the better guys, they don't need help because they already deliver for both the customer and themselves. The point is to make the mediocre guys better and thus help the customer, and hopefully also eliminate the bad guys altogether. If the 'system' only works when 'navigated around', its the wrong system!