sharpener

Vaillant data is all available in the Czech tables, easy enough to read without knowing any Czech.

3-phase is common in even small houses and flats in Germany so they would need to. Delta connection, no neutral. I had a Belling Lee cooker made in the '70s that for the export market had an elegant arrangement of busbars so the loads could be split onto the three different phases if required. Sadly expired 3 years ago, best cooker I ever had. Could do little things like use the top oven on the timer which I could not find in a replacement. All modern cookers seem to have fans to keep the controls cool which annoyingly run on for ages, maddening if you have a kitchen/diner. /reminiscence

Well there are ppl on the FB forum who are heavily into numerical performance stuff and HA (notably Mick Wall who has published many helpful articles e.g. this) and they don't seem to have raised any big issues about the Czech tables. And many others e.g. @Dan F who is active on this forum (and the Victron forum as well) who is technically qualified and talks good sense. Of course there are also the usual contributors of misinformation and general nonsense but hopefully I have got to learn the difference for the most part. I would be interested in further detail of how the UK market is viewed by Vaillant. I can see it must be a bit odd viewed from Germany particularly the shambolic regulatory setup involving the MCS. I have also to say as an experienced electronics designer they do not help themselves. Example: the internet gateway is mostly sold in the UK with a power supply card intended to plug into a boiler not an HP, rather than the one with a 13A power brick which is more expensive and needs a power point. Since the main controller can be and is powered off the low voltage ebus it would seem obvious to do the same with the gateway, which would remove the whole compatibility problem. Also the current generation of HP products has no way of receiving s/w upgrades in the field short of swapping out the main pcb, it is now 2025 fgs. Will be interesting to see if the new range has this.

Glad you found them. Even Vaillant SW Field Sales Manager did not know they exist. Have no idea why they do not seem to be available in English - or even German. For others here they are https://www.facebook.com/download/367541079323119/kl-06-e2-verze-01-18012023-2564719.pdf BTW I can confirm the 12kW is extremely quiet at less than about 80% output and not exactly noisy above that. Data seem to be accepted as accurate for the models sold in UK.

Vaillant FB forum has the famous "Czech" performance charts in the Files tab, shows turndown of all models (which is pretty good). The 10kW is a software limited 12, you might as well have the latter as the min o/p is the same but it would give you faster HW warmup if that is a concern.

Yes, the 10 and 12 are essentially the same. I have never understood the marketing philosophy behind this, maybe there is a max of 10kW or the corresponding max current draw in some particular market. As I recall there is some other special version for Spain. https://www.theheatpumpwarehouse.co.uk/wp-content/uploads/2025/06/Multi-Comm-M-Series-1-compressed.pdf data sheet not very helpful but shows the 9 kW dims are the same too. Google AI comes up with a forum snippet mentioning a min o/p of 4.5 kW for the 12 (which is a plausible but not very good turndown ratio). Some mfrs publish the refrigerant charge quantities for their various models, which might be illuminating if you can find them.

I thought the received wisdom was that defrosting is worst near zero but below that humidity falls off again so efficiency lost from that cause is not at the lowest OAT and so you don't have to account for it separately. Mind you my system is sized for Plymouth (-0.2C) so there is not a lot of difference, OTOH I have never noticed it defrosting either.

My money is on the PRV in the outdoor unit. It is a known weak component and you would not see the outflow.

I wonder does it just let the pressure down to zero, or does it dump a substantial quantity of water beyond that and so need a lot to refill? Might be a clue in how much air you have to let out afterwards. A pressure relief valve when tripped might not re-set and continue to let by. There have been quite a few reports of the PRVs in the outdoor unit being faulty and replaced under warranty, you might not notice that as IIRC the outlet goes into the condensate tray and thence to yr soakaway, that is where I would start looking. Unlikely IMO, in that even if your system is divided into circuits the return pipework will go to a common point so everything will be at the same static pressure irrespective of which valves are open.

Both inside the cover of the outdoor unit and elsewhere e.g. at the highest point of any loops, the furthest point of the rad circuit, the top of any buffer tank, near the expansion vessel, all manner of possible places. I even have one in the void where the HW cyl is, at the top of the feed to the coil.

Sorry for delay but this sounds more like it, can you give me a link for yr steriliser please @JohnMo ?

Have just come from a lecture/film about the chalk streams in Cambridgeshire and water use in new housing of which there is a lot. [Apparently the water abstracted from the aquifer lowers the water table so much that 20% of it has to be re-injected elsewhere to preserve the flow in certain chalk streams]. There is a big new development at Eddington on the W edge of Cambridge equipped with SUDS serving 8000 dwellings, the water is treated to render it suitable for non-potable uses (flushing loos, laundry) but the Drinking Water Inspectorate won't allow it to be brought into use. I asked what the underlying reason is, I thought such systems at household scale had been available for many years, what is the real problem? No-one seemed to know. Again, I mentioned our whole-house rainwater harvesting system citing 3 reasons it was not very practical for widespread introduction at the individual householder level: to get even the lower target of 80 litres/day per occupant you need about 50 sq m of roof per occupant where the rainfall is only 500 mm per year you need space for an underground tank it needs quite a lot of maintenance - filter changes, chemicals, UV lamps but these issues should be addressable at the scale of a whole housing developments. And again, I was told the DWI and/or Building Regs do not allow its adoption citing the difficulty of preventing erroneous cross-connections in individual houses. Can anyone shed any light on the truth of this and what might be done to improve the position?

Certainly worth doing, I have read on the FB forum several instances of leaking PRVs (IIRC related to a change of supplier, no doubt chasing a few p). While you have the covers off there is a cable run where my Vaillant service man put a drip loop to stop water sliding down on to a pcb, apparently this is an undocumented mod. I topped up to 1.5 bar 10 days ago and it is back down to 1.3, seems to go down by a further 0.2 in use (sensor is on suction side of main pump) but have not been able to find a leak so just put up with it.

Maybe I am not understanding your description but won't a few handfuls of fibreglass stuffed up the exposed bottom end of the boxing make a massive difference?

They bolted down mine, rawlbolts into a concrete yard area. I was happy to see this as the twin-fan Vaillants are quite tall and machinery can creep about with vibration - my bench grinder is a bugger for this. Actually they had to do it twice! They pulled the unit forward to do the rear connections (rear clearance is only 200mm) but forgot to push it back. I made sure they put epoxy grout in the old holes.