ReedRichards

Financially yes, that would be much better. Make the heat pump flow temperature as low as you can get it whilst still keeping the rooms warm enough.

But the exhaust vents to the outside and it is the exhaust that makes the most noise. I had an external oil boiler before I replaced it with a heat pump and my next-door neighbour still has one, although it's inside a little brick-built boiler house.

Unless your plumber squandered copper pipes unnecessarily, there will be a single flow pipe from your ASHP to a two way valve that is close to (and probably about half way between) your buffer tank and your DHW cylinder.

I presumed the valve being referred to is the one that controls whether the water flow is to the buffer tank or the DHW cylinder? So it's two-way valve and wouldn't there be flow even if it was stuck half way?

At the moment my house is showing cycles of power consumption which last about 20 minutes with flat-topped peaks lasting about 10 minutes and peaking at about 2750 W (give or take 100 W). I have a 12 kW LG Therma V so seemingly it can manage a good range of modulation. But I don't know if this scales down to the lower output models.

For what it's worth, my installer settings are the same; the pump capacity is set to 100%.

You might find more information in the document I posted here (Page 11, October 30, split into 3 parts).

If it's one or other then it should be able to heat the hot water without error or run the heating system with out error. If it's both then it's one of the 5 possible causes listed under "Heat and Tank Mode" (unless it's a valve problem that occurs when switching between DHW-"Tank Mode" and Central Heating-"Heat Mode"). The water pressure is good so that eliminates one of the five possibilities. That leaves: Strainers and filters blocked Water pump fault Flow switch abnormality PCB fault Don't worry about the WIlo pump for your radiators; that could be completely dead and the Therma V would not know. So it's not the problem; nor is anything on the central heating side of the buffer tank.

This might help:

I have an LG Therma V, not a NIBE. Since I am only paid for deemed export from my PV, there is little virtue in being economical with the PV electricity I use in-house.

I mean electrical power consumed, input power. My tank is heated to 50 C and to achieve this the output water from the heat pump is heated to 55 C (12 kW HP). It can recharge the tank in under 30 minutes but is consuming around 6 kW by the time the output water reaches its maximum temperature. I guess it tries to heat the hot water as fast as possible without regard to economy of operation.

Of course that's true, but my heat pump draws up to 6 kW when heating the hot water and that's more than my solar panels can provide. So my choice is between a 3 kW immersion heater which is completely free to use because I have solar electricity to spare, or using the heat pump solar-assisted for which I still have to import electricity.

I have an unvented cylinder with a pressure regulator on the rising main (and, I think, another regulator on the hot water). So hot and cold waters are at similar pressures. Perhaps the specified "at least 10 C above the required blend temperature" is to cope with the hot water being at a much lower pressure than the cold water? Now I remember, I did once have a problem with a mixer shower when the pressure regulator on the rising main was installed and set too low. I can't remember what went wrong but I remember the solution was to increase the cold water pressure a little.

If that is true then it's a terrible design. The whole point of running UFH with a heat pump is that UFH should not require a high flow temperature from your heat pump so you achieve the most economical operation. My retrofit system was designed for radiators and the maximum flow temperature is 50 C but if I had UFH I would be looking for a maximum flow temperature of 40 C or less. Also the water circulating in the UFH would make your floors uncomfortably hot if it was anywhere near 50 C.

I keep my tank at 50 C but the output from the tank is mixed down to a lower temperature, about 42 C I think. This is mainly because my OH deplores water that is painfully hot. We have three shower mixers and they all work perfectly well.

Although this is being marketed to ASHP owners, typically you want to run your ASHP nice and steadily, not at a few hours of high power followed by a few hours of low/zero power. My conclusion is either: Octopus don't really understand the needs of ASHP owners or This is just a marketing gimmick to find an excuse for charging a high rate for peak-time electricity.

In the case of our LG Therma V's, @ProDave, a flow rate error shortly after installation seems to be a "known bug".

I have only radiators. They respond more quickly to changes in the water flow temperature than UFH so are better-suited to night-time setback.

Do you have any paperwork showing heat loss calculations and radiator output? If you had then you might be able to see if something has been done incorrectly

If your 16 kW heat pump was underpowered for your property it would have been running at close to 16 kW for most of the day.

Okay, "cycling" is not an issue, short cycling could be. This where the heat pump comes on for just a few minutes then goes off again and this happens repeatedly. It's liable to give you inefficient operation because each time the heat pump comes in a certain amount of heat is wasted in getting parts up to temperature and it is wasteful if this happens too frequently and as too high a percentage of the total heat generated. Short cycling could happen if the heat demand from your radiators is too small, the return water gets too hot and causes the heat pump to cut-off. If everything it set up properly and working normally this could happen if the thermostat is set too low. But your problems imply that everything is not "normal" so no need to worry about short cycling as such yet.

I would say it was cheap, the cheapest readily available fuel for heating. Apparently the UK currently has 10 oil-fired power stations; time for some more.

So excessive that 300 l cannot possibly be the correct volume.

Here's a catalogue, which might help with identification: https://veranoconvector.co.uk/images/en/VK15-202006-EN.pdf . Perhaps you have a controller like the ones shown on page 40. I hope whoever calculated the size of your heaters took the low flow temperatures from a heat pump into account.

Fan-assisted heaters or the type that just rely on natural convection?