Dave C

All true, but if nobody's home after 8am, and no hot water being used, you wouldn't expect the tank temperature to drop any significant amount between 12:00 and 12:30. Particularly if everybody left at 8am and the tank was heated back up to full temperature just before 9am. Are you sure you don't have a leaking tap or similar anywhere? Only time my ASHP came on unexpectedly in the middle of the day last year it was because my daughter had left a hot water tap not quite fully turned off and there was a tiny trickle running out constantly - as explained above, it doesn't have to be much water drawn off before the sensor starts to see a drop. It would be consistent with the graphs - from 11:00 there's a slow but steady drop in tank temperature as the water trickles out, then the 'hot zone' in the tank is approaching the sensor so the temperature loss appears to speed up as the water continues to be used; then the heat pump kicks in to reheat the tank.

Depends how your pump(s) have been configured. If your pump(s) are set for the heat pump to control the pump speed - or if you have two pumps, but only one is coming on for DHW - then you might need to change the settings on the Ecodan; not sure what's involved in that. If the Ecodan is just telling the pump(s) to turn on, but not controlling the speed, then you'll be able to change the pump speed by turning a dial or pressing a button on the pump to switch it to a different mode. You'll probably need to find the user manual for your pumps; it should tell you how to find out whether the pump speed is manually set or not, and how to change it if it is. Regardless, you'll probably need to observe what the pump(s) are doing when the Ecodan starts trying to heat the DHW.

Certainly isn't what should happen! Some thing happened on my Ecodan after it was installed - heat pump would come on to heat up hot water cylinder, it would start heating OK, then in under half an hour would give up and switch over to the immersion, which I guess is the fall back behaviour for "we need hot water and the heat pump can't run for some reason". Turned out it was insufficient flow rate causing the heat pump to shut down - installer needed to reconfigure the water pumps. Could try turning the water pump speed up, if it's a separate pump plumbed in and it's just got a simple dial or push button to switch between different pump speeds.

Yes, absolutely - ASHP is set to heat my tank to 48c, and the mixer shower is plenty hot enough even after the tank has had most of the day to cool a bit. Don't know the exact water pressure, just it's "very good" according to the plumber and I'd agree. As mentioned above, some mixers might not be happy with the incoming hot being 42-48c, but mine certainly is. Feels unlikely you'd lose much temperature on your long pipe run if the pipes were insulated - just you've got the annoying long lead time to deal with.

I have an unvented cylinder heated via heat pump. Not Samsung or Joules, but the principle is the same... Setting the target cylinder temperature to 48c it works fine via a mixer shower (no pump in my case; mains pressure is plenty). Works fine when the tank has cooled a bit, too - I set the target temperature to 48c because then, even after 20 hours, it's still well over 40c and hot enough for a bath or shower, so I can just top up the hot water overnight on off peak rates. Mixer showers do tend to say the incoming hot must be a certain temperature e.g. 50c+. Mine says that but thankfully it turns out that's rubbish. I suppose maybe it's possible some mixers actually do always mix in a fair amount of cold and in that case you really do need 50c+ hot supply; I guess my example just proves that mixers do exist where 42-48c hot supply works absolutely fine (but unfortunately you won't necessarily find it out by reading the shower instructions/specs...) Maybe an expert can confirm whether all mixers are basically identical internally, and so they'd all work fine, or whether it's plausible that some will work fine and some not?

Might be worth bearing in mind that Freesat is a thing - I'm using Freesat currently because there was already a dish on the wall from the previous residents and Freeview reception isn't great for me. Also my (fairly new) TV has a satellite decoder built in, so no separate box required - plug dish into TV, done. Definitely don't watch enough TV to justify paying for cable or Sky By no means always the easiest option, but if Freeview reception is marginal it can sometimes be a good workaround.

Agreed. So many potential sources of inaccuracies here! If the electric meter didn't change reading when the immersion was on, then does that mean it only 'ticks over' when a whole number of kWh is used? In which case your heat pump used perhaps 1.01-2.99kWh of electricity, you can't be sure exactly how much. If the temperature sensor measures to the nearest degree, a 3 degree increase could be anywhere from just over 2 to just under 4 degree increase in reality. Except it's worse - the hot water tank is almost never the same temperature throughout. The water next to the sensor might have increased by 2 degrees, but that doesn't tell you how much energy has gone into the tank, because you haven't raised the entire tank's temperature by the same amount. If you have the entire tank at room temperature, then let the heat pump heat it up to full target temperature, you'll have a better estimation of how much energy has gone in, because at least then you know the starting temperature of the whole volume, and your rounded electricity usage will be off by a smaller percentage. Still won't know exactly - depending on where the sensor is, if it reads 45 degrees, might be a bit of the tank below the sensor at a lower temperature, and possibly the majority of the tank at over 45 degrees.

Thanks, that's good info - COP of 4.8 at below freezing temperatures is really encouraging! At the very least it shows there's some A2A options out there which keep a good COP at low temperatures. Still interested to see how well the electriQ holds up - that note about performance dropping off below 5C is still a bit suspicious...

That looked interesting until I saw the note in the documentation about it switching to purely resistance heating at 2C and below! Same question applies to the electriQ - it has a note about heating performance dropping off below 5C. But by how much?! I don't really care so much what the heating COP is when it's 10C outside, don't need much heat input then, the COP when temperatures are approaching freezing is much more interesting...

It was this scheme which I see has just finished, so nobody will be getting it after this month alas!

Also a Lux, with 7.2kWh of Pylontech batteries. No solar - just making use of Octopus Go off-peak cheap rates (although if off peak rates become less favourable in the future, installing solar is a possible next step). Since I also have a Lux... -Yes, you can set multiple charging timeslots, although I only use one of them (00:30-04:30 Octopus Go). Well, except on the one day per month that Octopus gives me an extra hour of free electricity then I use the second timeslot for that day. -It then defaults to being primary power source until empty (or until a certain charge level, so you can choose how much power to always hold back for a possible power cut) -The default offering is that you get a double plug socket hanging off the inverter that's continually powered including during a power cut - it doesn't feed the whole house. When I had mine installed they did offer the whole house switchover at additional cost, but I didn't bother to go for that (and I can't see it's on offer on the website now). Cost wise, prices have increased in the 8 months since I had mine installed so you're best just checking the website! https://homeenergygroup.co.uk/lux-ac-battery-storage-greenlinx/ I was pleasantly surprised that the cost on their site was indeed exactly what I paid, no hidden extras. (Shouldn't really be surprising, Yes, in my case - since I have the same system as Alshamal, my calculations were very similar The system and batteries have a 10 year warranty, and the expected cycle lifetime of the battery means they should still be usable at ~12 years. Since the entire system will have broken even at 7 years (hopefully!) that means a good few years of banking savings before the batteries start degrading to the point of needing replacement, or the inverter fails and incurs costs. In principle...

That's probably fair - I have a battery, but initially made the mistake of comparing the Cosy price to my current Octopus Go prices; of course prices have gone up since my last renewal! So you get two shots per day at charging your battery, and the price is higher than Go, but less than double. Working the figures out, for my battery I reckon Cosy is cheaper than Go on days where I'd use ~20kWh or more. That's essentially never during the no-heating part of the year, but during the winter ... eh. Probably a bit of a toss up: in January, that's the majority of days for me, probably about half the time in December/February - so for those three months, it's better than Go. The other 9 months of the year (especially when there's no heating going on!) it's worse. If you were willing to switch to it just for the winter months ... yeah, it could work.

My mixer shower says the same, but echoing the other feedback - it works fine with the hot water coming in at 48C (or realistically a bit less, given it's only 48 when the heat pump has just finished). Did have to tweak the temperature adjustment on the mixer up to its maximum, though.

Well, it's a 5kW heat pump (so probably not too big!), and I'm not shutting any radiators down so full system flow available all the time. That only leaves "I need a buffer" - but does that actually improve things that much? If the heat pump's coming on for 3 hours, then shutting off for 3 hours, am I actually losing that much efficiency? It's not short cycling, after all...

That might be the ideal, but in practice neither I nor the other two heat pump owners I know have ever managed to get things arranged so the heat pump just runs constantly at a low power. Perhaps that's because it's annoyingly uncommon to get load compensation (rather than weather compensation), or because on a-bit-cold-but-not-freezing days the heat pump just can't modulate low enough to do anything else, but the end result is that except on the coldest days (and even after all the tweaking I've made to reduce short cycling), my heat pump comes on for 2-6 hours, then the house is up to temperature and it shuts off for a while. It's not ideal but it's what's happening - so I guess you could regard this plan as a pragmatic acceptance of that pattern, saying "if you're going to have the heat pump running for 2-6 hours on 1-4 hours off anyway, why not play with your thermostat to get those hours to line up with not-peak-time". Having to pay those peak time rates during the summer, though ... it's more like 7 months of the year for me, that I don't need any heating, so while in principle this plan isn't a terrible idea during winter, having to switch onto and off it every winter (and hoping you don't get stung by a more expensive rate every time you do) isn't appealing.