JamesPa

It will stop altogether if it detects flow rate too low. Mine did when the filter bunged up. BTW I suspect the mesh filter, normally fitted near the return inlet, has a fairly high pressure loss even when not bunged up. If yours is like mine a model with a larger area may well assist!

Is the heat pump actually complaining. If not leave as is and allow deltat to rise a bit. Or fit an auxiliary pump slaved to the heat pump one, but no buffer. Either is easier, cheaper and will likely give better performance than an unbalanced buffer,which is probably what you will end up with.

Im also interested in this thread as Im having (yet) another try at making the battery business case work (so far I haven't been able to). I have 4kW peak PV, a heat pump and an EV and currently get paid 16.5p for export and pay 7p (midnight-7am) or 26p (7am-midnight) for import. With the optimisation possible in the absence of a battery, that makes quite a challenge for the battery business case, although its close. Judging by the price on the Midsummer site, Givenergy AIO hardware alone looks expensive compared to quotes I am currently receiving for fully installed systems; Is it worth the extra or are there deep discounts available?

The really sad thing is that the question in the title is worth asking! Is says a lot about MCS

None of which will add any value and, if a buffer is fitted, will increase running costs. @Dillsue the advice others have given is sound. You don't need extra kit you just need to balance the kit you have and readjust the WC if necessary so you can operate comfortably with thermostats and trvs at max. You need to forget everything you were taught by manufacturers of add on controls about operating boiler based systems, it wasn't really true for boilers, and definitely isn't true for heat pumps. It needs a leap of faith but once done you should get a house that's much more comfortable than you ever will with a boiler and lots of fancy but irrelevant controls.

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).