@denevil That is interesting on my volumiser I can see that an immersion has been installed but there is no wire attached to it so completely disconnected!

I have one of the Heat Geek affiliated engineers come over at the end of next week to have a look at the system and perhaps I will learn some more about what needs to be changed

One thing he did say from the pictures is that the main flow return pipes should have been 35mm given size of install.

Important was that box EP001 was wired and it turns off the master valve supporting DHW prioritisation (which it wasnt at first) ... this now works and DHW is heated from primary circuit.

Enabling the immersion does seem to help reduce defrost cycling but as its been bit milder I cant see for sure how much ...  but my daily electric bill is 40 to 50kw for last week which seems better than before ... need couple more weeks really

@soniks I think they are sometimes not wired up on the Grant installs. Mine was, but I recall the installer saying he was not supposed to enable it using the controller parameters. The volumiser includes a relay inside which is controlled by the ASHP unit, so as well of 240V power cabling to energise the heater there is control wring required between the ASHP monobloc and the volumiser. This is for control and interlocks - to enable/disable the immersion heater based on control settings.

I had a play with mine, and set the immersion as supplementary heater during low outside ambient, using the parameters suggested by Grant in the volumiser installer document, as a way of boosting the installed ASHP capacity by 3kW. It didn't work as intended. The heater energised, but the ASHP turned itself off once the heater had energised! So instead of around 8-9kW from my 10kW ASHP in low ambient, plus and extra 3kW, I was getting only 3kW from the immersion heater. I didn't bother trying to work out why it was doing that. I just wanted to see if it would work. It did, but not as a supplementary heater, as a replacement heater.

First picture shows a symbol not in the manual (as far as I can tell) so wondering if this is the supplementary heating in defrost cycle.

The next page shows the two tables one for defrost assist and the other where the immersion can be used as primary heat source eg if ASHP fails.

This section says connect immersion control signal to terminal 46 in ASHP

Posted by: @denevil

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Important was that box EP001 was wired and it turns off the master valve supporting DHW prioritisation (which it wasnt at first) ... this now works and DHW is heated from primary circuit.

Enabling the immersion does seem to help reduce defrost cycling but as its been bit milder I cant see for sure how much ...  but my daily electric bill is 40 to 50kw for last week which seems better than before ... need couple more weeks really

 

Looking at the first photo, how many pipes are connected to the volumiser?

If there are more than two then it is more likely a buffer tank, which could be a source of problems. I would suggest that you identify the pipes coming from and returning to the heat pump, and also the flow and return pipework to your heat emitters. If you have a suitable thermometer then measure the temperature of each pipe and post the results, ensuring that you have good thermal contact and use insulation to get accurate readings.

Did your installer forget to insulate all the pipework? 🙄 

there is a single pipe in which is primary from ASHP and a single return pipe ... primary circuit is on the right as you face the LLH .... secondary is on the left 

out of the LLH is a single pipe for secondary circuit with a single pipe back for return.

the secondary feed splits to two loops ... one for rads with its own pump, and one for UFH with its own pump

the design is exactly as per Appendix A S plan in ASHP manual using DHW prioritisation

Plumber did come back and insulate all the loft pipework ... all the pipes in the floor were insulated (I checked before they were covered) .... he will finish off insulating pipes in cupboard when next back.

I am happier with the system than I was a week ago ... fingers crossed the immersion help in defrost has stopped the cycling.

We average 18kw per day elec use, so with the new smart meter showing me 40 to 50kw per day thats 22 to 32kw per day heating and hot water in the last week.  Heating the hot water in day time I think also helped as it did struggle to get to 55 degrees when it was frosty out.

@soniks unfortunately this wasn't an option for me. Just googled a level 3 monitoring system and it would be about £1200 for both pumps from what I can gather to retrofit and says it can drop the pressure? Think I'll have to give it a miss unless there's a cheaper alternative out there.

Posted by: @bretix

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unless there's a cheaper alternative out there

There is, and it's non-invasive to boot, but it means buying from China:

https://www.aliexpress.com/item/32810573624.html

You have to be very careful to make sure you select the head unit plus the right size clamp on sensors (TS2 transducer for DN15-100mm, DN is pipe Diameter Nominal), but it will only set you back around £110 including carriage. You also have to get and set up the temperature and meter sensors but there are relatively inexpensive. Guesstimate cost per circuit monitored in the order of £250 (plus many many hours of head scratching...).

I haven't actually bitten the Chinese bullet yet, but others on the forum may have.

@soniks how do you compile these graphs? is there any information available on this? Thanks!

@soniks I guess this is a late reply but I've got the 17kw Grant Aerona the same as you and I'm running it with underfloor heating in a 5 bedroom house with two large open plan rooms, and it isn't that well insulated by any standards. The UFH itself runs extremely well though I had some initial problems because it is a slightly unusual self-balancing system. Now that it is working it heats the house really well. It is a retrofit polystyrene but it goes from about 16 to 18 degrees in two hours at around 5 degrees outside temperature, so it is quite rapid. If you can, I would do it. Lovely not having radiators on as well and the heat is ambient so it is never stuffy.

We had the engineer out today. Turns out our weather compensation wasn't set either. Though everything has been working well it has been expensive and when the temperature dropped, around the time of your initial post we were at about 73 kw/hr. I'm really hoping the weather compensation helps to improve efficiency when it isn't so cold outside. On average under 10 degrees outdoor temperature, we are around 50kw/hr.

Our flow/return was also set at 30/35 and this was upped to 40/45 which made a big difference.

I'm not sure if this has been a problem but we've had some issues with the hot water priority where it often overrides the hot water, which sometimes struggles to get to 50 degrees, especially at low temperatures. It really messes with the heating and is a bit annoying when not using the hot water at all. Since we have a pump running the hot water around constantly, this seems to cause the hot water to drop a couple of degrees every hour and then the pump kicks in to heat it back up. I'm considering a timer for the pump for the hot water circulation.

@allyfish Interesting would be a good option as a backup should the ASHP were to fail and we needed at least some minimal heating in the colder months