sharpener

Bread knife.

Those inline filters get blocked quite easily. In slow time it would be better to bin it and get a Magnaclean or Adey HP filter fitted indoors, they have a much bigger element like an enormous kettle fur collector and a magnet for collecting magnetite particles shed by the radiators - which you should not be gettting if there is adequate inhibitor in the system. Gledhill cylinders have a bit of a reputation for noisy internals, I have seen it reported as a specific quality control issue in the factory.

As installed mine had a compliant 22mm D2 setup taken into a first floor soil stack via a Hep2O bladderless trap. Thinking this was where the restriction was I modified it so there was first a 2.5m drop to the ground floor and the trap went into the stack at that level instead. But it is not much better and will still not take the full flow from the tprv. So I think that the whole concept that the pipe below the tundish needs to be only 22mm - one size up - is flawed, the regulations do not achieve their aim and are pointless. And a tundish hidden away in an airing cupboard slowly filling with water is NFG either. Personally I think it would be better to have the relief valve piped in 15mm directly to waste with an electrical or mechanical alarm to indicate there is something wrong and possibly a small air admittance valve to vent the pipe but prevent smells. As a further twist the MCS surveillance visit on another house meant the HP installer was called back to move the tundish to somewhere slightly more visible (even though it was pre-existing and not part of his work). The D2 pipe is 28mm bc of the run length but has a 28mm tundish that will overflow too. So the modification is purely cosmetic, the tundish is still in an alcove off a loft above our bathroom, access is still via a ladder and a door which is kept shut so we will neither see or hear any overflow condition. Which is why I test the tprv whenever I am up there, at least I know it is not stuck and the valve seating is washed clean.

But they are ineffective. My installers met all the requirements on paper but the regulation tundish is too small to contain all the splashing. But more seriously, at full flow from the tprv the water backs up in the D2 pipe and would overflow the tundish if I continued the test.

I have an OSO cylinder fed from a rainwater harvesting system and it suffered from low pressure which I thought was the crap Stuart-Turner pump. Turned out the inlet reduction valve spring had been corroded away by the acid rainwater and was providing no counterforce for the valve. OSO could only sell me a complete valve block but a 3rd party dealer had a replacement Reliance cartridge which was a lot cheaper. The next fault to come along was the pump, cracked plastic impeller shroud. S-T regard them as unmaintainable but I had the bits of a previous pump which had failed with a leaking shaft gland so was able to fix, no thanks to S-T. Will buy DAB if it fails again, you can get replacement glands for them. Other house has an Ariston cylinder with ?their own valve group which has a mesh debris screeen in it, MIs say to check this annually and I do this though I have never found anything significant in it. +1 for always giving the knobs a twist when I am up there and it is always reassuring to hear the water gurgle away proving the D2 pipe is not blocked with spiders.

All sound advice. Should last for 5 years without probs. Have just taken an expansion vessel out of service as too small for new heat pump. Originally installed in 1995 and still in good working order. As well as the checks outlined above if you get a new one fitted make sure the precharge level is adjusted properly. Mine was left at the factory setting which like yours is 3 bar. This is too high for a system pressure of 1.5 bar and will mean the pv does nothing, the precharge needs to be about 80% of the working pressure as said upthread by ?@Beelzebub.

Yes but unfortunately the 7kW Vaillant unit has a poor reputation on account of the defrost performance, the others are much better. ETA @ectoplasmosis might not agree.

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.