Yes our Mitsubishi let’s us control the heating and hot water separately.

That said we probably won’t turn the heating off - it is controlled by a wireless temperature sensor in the main living room with a daily target temperature schedule in the heat pump. If we get the odd cold day in summer then happy for the heating to turn on.

Had considered turning HP off entirely for summer but reasonably sure it’s more efficient to heat water with heat pump from Solar pv than using immersion from solar pv. I’m planning on measuring the two approaches this summer - the HP uses 600 Wh a day in idle which is probably about a third of the energy needed to heat our water. We will see!

I’ve never turned ours off. It’s controlled by thermostats in 3 zones. Turn down the stats if you don’t want it to run. Mine does DHW too so it works all year for that too.

will just let the stat do the job for the next month. once it gets to may, may well set the heating zone's mode to "off" , at that point you can get days where its 15C or 16C air temp but "feels warm" , you have windows open and you don't want the heating on ... a stat based approach could still come on at that point. But still let it run DHW. I doubt I will go as far as turning the heat pump actually off at the isolator - assuming that's not what you mean?

If I get as far as fitting cooling capable emitters in the bedrooms that overheat due to solar gain, I'll be putting it on in July/August in cooling mode as/when the next heatwave arrives!

I turned my central heating off last summer leaving just the DHW  set to on.  However the MelCloud still showed a regular daily use of energy under ‘heating’.  Confusing, annoying and I don’t understand why.

My Daikin wall programmer has a button that allows you to switch on or off the space heating independently of hot water; both are separately programmable also. I switched off the space heating on March 23rd (I'm in Italy, and spring has sprung). One interesting (to me at least) thing I noticed was how electricity consumption changes with various definitions of 'off'. We were away for a week in January and I switched off the space heating (I realised I shouldn't have, but it helps this story along) using the referenced button, and also switched off (via the programmer) DHW production; we don't run a legionella cycle. So the unit was essentially available to function but wasn't being told to actually do anything - standby, if you like. Our daily consumption while we were away was a fairly steady 6.8kWh. This I assumed was our 'background' consumption - fridge, lights on timers, and the heat pump and other electrical devices on standby. We were then away over Easter, and I thought I'd switch off the unit at the consumer unit - all power cut to the Daikin units (we have an outdoor and indoor unit) and the programmer while we were away. Same fridge, same lights on timers with same timings, same electrical devices on standby other than the Daikin units - only difference was the power being cut to the Daikin units. Daily consumption was a fairly steady 3.8kWh. Could the Daikin units (outdoor unit, inside unit, programmer) be using 3kWh a day just idling and doing nothing constructive whatsoever? We have solar but it feeds only the ASHP kit which is on a separate power line (we have an odd setup), so the difference is not down to any increase in solar contribution to overall consumption in March versus January. I confess there might be something obvious I'm overlooking here...😀 

Posted by: @marzipan71

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Could the Daikin units (outdoor unit, inside unit, programmer) be using 3kWh a day just idling and doing nothing constructive whatsoever? 

quite possibly. when you do the maths, thats 125W on standby, which is not out of the question. there's a lot of discussion in various places about what are the standby consumptions of heat pumps  - there is a lot of inconsistent information about and I don't think there are reliable, standarised, universal mfr published figures (like there are for domestic appliances such as TV's).  Another issue is that its not trivial to measure. CT clamps are cheap and easy to fit , but may well not be accurate enough due to "Power Factor". Proper inline meters will be accurate but more costly and disruptive to install.

Posted by: @morgan

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I turned my central heating off last summer leaving just the DHW  set to on.  However the MelCloud still showed a regular daily use of energy under ‘heating’.  Confusing, annoying and I don’t understand why.

Unless you have external metering the Mitsubishi 'indicative' consumption figures are rubbish when the heat pump is in idle.

Been discussed here: https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/mitsubishi-8kw-strange-energy-use-readings/paged/2#post-18181

They know about it but don't seem to be that bothered.

@steevjo Is the external metering MMSP that I've seen mentioned?  If so that in itself is expensive to have fitted isn't it?

However our meter readings are hellish high.  A predicted electricity usage of £5k this year!

@morgan Yes, could be. MMSP refers specifically to the Model Metering and Service Package which was part of the now ended Renewable Heat Incentive (RHI) scheme. MMSP monitored the electrical input to the heat pump and its heat output - the numbers were supplied to Ofgem and you were paid around £50 each quarter. Some heat pump installations had to have MMSP to qualify for RHI payments.

however external metering can be fitted that is nothing to do with MMSP. For example I’m considering fitting one of these to monitor the energy going to the heat pump

https://shellystore.co.uk/product/shelly-em-2x50a/

its not necessary - the Mitsubishi metering provides results I can believe for 6 months a year - the CoP is fine, it goes down when things get cold and my electricity bills are ok. I know the heat pump isn’t using what it says it is in summer from my bills/usage.

But I’m a bit geeky and would like to see what’s happening the rest of the year too.

I have no intention of getting a plumber in to fit a heat output meter - a step too far for me. Pretty sure heat pump is working reasonably well so don’t see the need.

I just don’t track bother tracking the CoP from May though September.

Hope that helps

Here’s an example of a mid certified meter- if you have a spare slot in your consumer unit, it’s an easy install for a sparky, split core so just clips on the heatpump wire!

Posted by: @morgan

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However our meter readings are hellish high.  A predicted electricity usage of £5k this year!

£5k sounds a lot for an 11kW heat pump but no way to usefully comment without lots more info - maybe start another thread?

Some questions: predicted use, what was actual use last winter, what other electric demand do you have, eg EV? room temperatures? EPC heat demand? Control system? Hot water details, typical flow temperatures, cycling?

Good luck