sharpener

Assuming you already have a public water supply of potable quality, you have six months to ask yourself the question "Starting from scratch do I want to pay >£1/week to get the additional bacteriological protection or better taste (if any) that this gives me?"

They are mandatory or nearly so i.e. electricians will want to fit them citing MCS rules. They need to be outside the prohibited envelope for a R290 (propane) HP which is why in the pic it is just above the top of the HP. The theory is they are needed so they can be visibly padlocked off for operative safety during maintenance. I don't know why a padlockable isolator, rcd or two-pole mcb indoors is not thought to be adequate, as it is for other appliances. To my mind they mean un-necessary connections requiring an extra outdoor enclosure which is ugly and an extra expense. If they are truly necessary they should be designed neatly into the HP enclosure itself. There is an alternative school of thought that says they need to be next to the HP so it can quickly be switched off in case of fire or other emergency, I believe this is an urban myth. Mine is padlocked on as it is sited right on the path to the house and near a public highway. Mainly as a deterrent, it would be easy enough to break/cut through the plastic to turn it off in a genuine emergency.

Depends. It will not improve the modulation range of the compressor, just restrict the use of the top part of the range. It might reduce any temp overshoot if you are seeing that at any point. You might find there is a mains current limit setting which will have a similar effect. In addition to NR I have this turned down to the min of 20A, as some of the time it runs off my battery storage system which can only provide 4.4kW for everything in the house. NR mode might improve CoP for DHW production, the restricted power means less of a delta T between the flow in the coil and the body of the cylinder. So higher CoP as the HP runs at a lower flow temp. Vaillants have a DHW Eco mode which does this as well.

You are just reading its state from an info field in the DHW settings. To change it to Not Connected go to Installation config|Heat pump control module config|MO2. See the simulator here https://simulator.vaillant.com/vrc720/at/#/simulator. Don't agree with that. What evidence do you have for it?

What time is that? Most E7 tariffs are cheap until 0700, same for Cosy. If (only if) your sensocomfort is it a suitable place then active or extended can work out better esp. if you have solar gain or other internal heat sources. Adaptive will subsequently keep it tuned to the right curve. More peace of mind than any big further improvement. MO2 is a mulitfunction 230V output on the Appliance Interface for various kinds of external pump, if you don't have one set it to Not Connected in Installer settings. I doubt it will. Adaptive will eventually settle on the optimal heat curve. Is displayed on the App. Also on the VWZ AI (not the sensocomfort). You can see the no. of starts as well, if less that 3x the hours run (i.e. avg of 3 starts/hr or less) nothing to worry about, take up macrame instead.

Many ppl would think cycling less than 3 times per hour is fine, my 12kW Vaillant cycles like this in mild weather but I am not angsting about it. +1

Looks like the compressor is cycling on and off bc the heat demand is less than the min it can modulate to, and the circulation pump flow rate is following that. Not a problem in the absence of other indications or error messages IMO.

Fortic tank, common in flats before UVCs. Hence poor head (1 m if you are lucky) and need for shower pump. Replace with UVC, all sorted. Use E7 if you can get it back, otherwise you will need a smart meter and their ToU tariffs.

I think you have answered your own question pretty definitively! If it ain't broke and all that...

Good find. Should be required reading!

See this thread which I have already linked you to so no new information. Did you get a quote for the HX kit? I am interested to know what they cost. IMO this will be the best technical solution.

The diverter valve may appear to be working externally but if Honeywell they have a tendency to fall apart internally and bits can end up in odd places in the system. Do a search on the Vaillant FB page, lots of threads about this. I suggest you get some pipe freezer or hire an electrical one and then take it apart to check it thoroughly. If broken replace with another brand e.g. ESBE or Drayton, you might be able to get one on sale or return. Fit the missing flow setter at the same time! Your "whoosh" might be flow through the automatic bypass before the zone valves/diverter are fully open or after they have shut. This happens on my system. These are likely to be antifreeze valves, are they like the this picture? In which case the glycol may be superfluous and so you don't need the pipe freezer.

I would suggest a few more things based on limited (so far) experience with a 12kW Arotherm Plus. Especially as your bedroom tends towards being too warm at night I would suggest using a scheduled setback at night to 18C. You might see a slightly worse CoP but the total energy consumption could still be less. If that works you might even try Eco (= off at night). With such a small heat loss and a relatively powerful HP it should have no trouble in bringing the temp back up in the mornings. This will also reduce the parasitic losses. But they are not very big in any case, mine reports just 11W in idle mode (controls are a few W in addition I think). Setting Adaptive = on and Room Temp Mod = Extended may make marginal improvements The HW algorithm is a bit weird, you could try reducing the cylinder offset to zero. It may not make much difference. Make sure the HW is set to Eco on the Heat Pump Interface Unit (not the SensoComfort), this will reduce the peak flow temp and so improve the CoP, You might then need a longer heatup time than 90 min as you have a big tank, or split it into two periods depending on yr tariff. I strongly suggest reconsidering the legionella cycle, it seems to be making quite a big hit, for most ppl it is not necessary, there is a useful article on the Heat Geek w/s. You have got (HW) Circulation pump = On. Not clear why this is, as MO2 is Not Connected. If you do have a secondary circulation pump you can give it its own schedule so it is only on when it is useful. If you haven't then this setting is not meaningful anyway.

Yes, very deficient. Tried it again just now, sometimes the Next button was not there, sometimes it did not work. It would be useful to see what info it drags out of the EPC. I suspect not much or it would already know the floor area when you try to modify things. CBA to try and reverse engineer it any further but agree it could be a lot better. Tried Good Energy estimator, seems to download floor area and type of house from EPC, not much better though, quotes me for 2 x 12kW Midea, £20700 less grant, not remotely competitive.

I think OP is in N Ireland so quite mild. I have trodden this path ahead of you and agree with this opinion, see this thread for full gory details. Heat exchanger a better technical option, less disruptive to install and prob. cheaper than the marginal cost of upgrading the tank even if you can find a buyer for the old one. However it will be interesting to see what the kit costs, it is based on a SWEP HX, reputable brand, lots of further info here, water needs a pH of 7.5 or more to avoid corrosion (which my rainwater supply can't meet).