ReedRichards

There may be difficulties combining a solar diverter with a battery. You probably don't want the diverter to drain the battery when the sun goes behind a cloud. But if you, for example, boil a kettle and the battery contributes to the power required then when the kettle switches off the battery does not switch off its output instantaneously but ramps down its output. To do this it briefly exports energy to the grid. An over-zealous diverter can see this brief export as excess solar power, engage the divert and drain the battery.

Yes and no. An immersion heater requires 3 kW of power (maximum). That is well within the capability of my solar panels when the sun is shining, even now just about. So you can heat your water for free. And I can make the water hotter than my heat pump can manage so it lasts longer. When my heat pump is heating the hot water it works its way up to in excess of 6 kW (total load on the house) to get the water up to 50 C. Even with my battery and panels working together I am unlikely to achieve 6 kW of output power. So my choice is between completely free but inefficiently produced hot water using the immersion heater or efficiently produced but costing money hot water using the heat pump.

Shoemakers. I have the heat pump controller and an app controlled switch wired in parallel. I have never had them both on at the same time but I see no reason why that would cause harm (and it's easy to avoid). About a day after my heat pump was installed it went wrong and the error state prevented me from using it to control my immersion heater so I could not even get hot water. This was unacceptable! So I got the electrician back to wire a switch for the immersion heater in parallel so I could use it even if the heat pump was out of action. Any rational installation should be done that way. Now I have an app-controlled switch with a timer but which I override manually if the sun is not shining. Edit: Just to be absolutely clear, my immersion heater is on its own dedicated circuit with its own dedicated circuit breaker in the consumer unit. So parallel really does mean parallel. When my heat pump turns my immersion heater on or off it must use some sort of logic controlled power switch, not power from its own supply circuit.

Hold the Left Up arrow and the + button simultaneously for 3 seconds to enter the parameters settings menu. You can then set the number of cycles per hour ("2CR"), try 3 instead of the default 6. And the minimum on time ("3OT") - which unfortunately is limited to 5 minutes maximum but better than "a minute or so". https://livewell.honeywellhome.com/honeywell_wp/wp-content/uploads/Resideo_T3R_manual.pdf

My monobloc ASHP has an outside pump that sends the water to the buffer tank or the DHW cylinder. And there is an inside pump that circulates the water around the central heating system. The outside pump is responsible for any defrosting necessary and is completely silent inside the house. The central heating pump is pretty quiet but does make some noise when the central heating is on. But the pump is small and so might be positioned away from the buffer tank where the noise it makes is not intrusive. If you must have a buffer tank, just insist that no pumps are co-located with it.

You would get central heating when the DHW cylinder was calling for heat and your water would be heated when the room thermostat was calling for heat. But that is only if the wiring was "right" and the 3-way valve was "wrong". So long as the wiring matches the valve orientation I don't see that it matters which way round it is.

I plumbed my heating using an F-Plan but it just got thinner and thinner.

Potential problems: Not all heat pumps are accompanied by good documentation and instructions or have the installation instructions readily available. My heat pump ran for 24 hours and then went wrong. My installer came back promptly and fixed it. Subsequently he gave me a copy of his installation and training manual which explained the likely causes of the error code (a blocked filter in my case) but I think he got that by attending a training course; I have never seen an online copy. You probably need a buffer tank so you'll need to work out how big, where to put it and how to plumb it in to the system. Buffer tanks confuse me. You will need to work out how to size your radiators/UFH (and their supply pipes). You can find software to do this but I tried and gave up because I did not know how to calculate all the correct input parameters. There is likely to be enough advice available here to overcome all these potential problems but heat pumps are unfamiliar to most people and most plumbers and so there is plenty of scope for error.

Grant suggested I get a hybrid but then helped me to establish that it wasn't necessary. These days you need to be able to adjust the choice between oil boiler mode and heat pump mode according to the relative prices of oil and electricity.

But not on this thread, you posted that question elsewhere.

An MCS registered installer should have some software that will perform the heat loss calculations. In due course you should get a full report of the results, not just a summary. If the right information is input then the conclusions should be broadly correct. However some factors such as solar gain or wind chill are not taken into account.

It's such a pity that you are new build and cannot get RHI. Not just for the money but because you are obliged to use an MCS accredited installer who is obliged to perform detailed heat loss calculations that tell you not only what the heat loss from your house will be but how much heat every room needs. You are stuck with a builder who may or may not be making his calculations with the same degree of rigour.

I thought the companies offering a Grant heat pump were being over-optimistic about savings that this could achieve by comparison with my oil boiler. Nor did I like their impersonal service using teams of fitters roaming Scotland. And I wanted more than just a heat pump and radiators, I also wanted to re-route a lot of my heating pipes. So I went with a contractor that could offer me a personal service, quote for all the work I wanted and was prepared to admit that it was a close-run thing to save on running costs. By the way I see nothing wrong with TPI per se but you have to be able to limit the number of cycles per hour. I was just helping a relative set up an oil boiler controller with TPI and I set it to 3 cycles per hour because an oil boiler is another type of heater that you don't want to be on for just a few minutes at a time.

Grant is a UK manufacturer; they gave me a quote when I was looking for heat pump in 2020. They were also the favoured choice of two Scottish companies that (over?) sell heat pumps with teams of fitters to do the installation. Possibly Grant heat pumps are not terribly sophisticated because oil boilers are not terribly sophisticated. They also make aluminium radiators (of which I have two).

I don't mean to bang on about this because nobody agrees with me but let's compare my installation. My Heat Loss Report assumes an outside temperature of -3.7 C, calculates that my building needs 8.95 kW and prescribes a 12 kW heat pump. Then there is another 9.3 kWh per day for hot water (which must be an average of 0.4 kW). You could say that this give me a safety margin of 1.65 kW or you could say that this puts me at 86% of my maximum output capability. All this derives from an MCS-accredited evaluation for RHI. My impression is that @Tim S is looking for a lot more headroom than I have. The problem with headroom is whether your heat pump can modulate down enough to avoid cycling in warmer weather.

Hang on a minute. 6 kW seems to be what you need when it is -10 C outside and you spend the day taking one hot bath after another. So almost all of the time you should need a lot less than that. I have seen some figures for a Mitsubishi Ecodan which seems to suggest that they are most efficient when running at around 50% of their maximum output but less efficient at the high and low ends. If you need 6 kW for -10 C then you need about 4 kW at 0 C and so for the vast majority of the year you will need less. Could 6 kW actually be too much?

It's a bit of both but more water noise than vibration, I think.

Yes, the thing I like least is about my ASHP is that the central heating is audible whereas with my old external oil boiler and external pump it was completely silent. Now the central heating has its own internal pump and there is a bit of noise from this and also noise from water inside some radiators, presumably because of the high flow rate that ASHPs like to use in order to maintain a small temperature differential. This noise is not loud enough to wake me up at night and it's not entirely bad to have some audible feedback that the central heating is running but I would rather it was not there. It's the radiators nearest the pump that are noisy, the others are silent.

Any ASHP that I know of will automatically crank itself up (in output water temperature) to heat the DHW so no need to lose sleep about that.

You get very little documentation with the LG! If I look at the graph of power drawn by my house I occasionally see little blips in the middle of the night when everything else is off; I wondered what those were. For me this is quite a rare phenomenon, presumably because it does not often get cold enough. This water circulating pump is inside the outside (monobloc) unit and I am sure this makes no audible noise inside the house.

My buffer tank is underneath the hot water cylinder and integrated with it. I had assumed this was a commonplace solution but perhaps not.

No worse than the external oil boiler I had before the heat pump.

I wonder if the poor client had been told that the ASHP would be cheaper to run than their old gas boiler?

I don't think so. An ASHP is viewed as electrical heating and scores badly on the EPC. EPCs fail to recognise the energy efficiency of a heat pump, AFAIK.

I know next to nothing about them but it seems you can now buy "Low Temperature" gas boilers which operate in the same sort of temperature regime as a heat pump, particularly a heat pump serving radiators and are more efficient than a conventional gas boiler. So you might want to consider getting one of these with suitably sized radiators and benefit from the current lower running cost of gas heating but having something that is more "heat pump ready" when you need to replace this gas boiler and gas boilers are no longer sold.