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Twin 10kw Grant Aerona Volumiser Tanks using lots of power

adam · 2025-02-15T13:50:38Z

Hello All This is my first post but I have been lurking here since our 2x 10kw Grant Aerona's each with a Grant external volumiser tank were installed mid last year. We are in the middle of a renovation of a 1960's property, a bunglow with an unheated basement. We have completed the roof, structural and first 50% of occupiable space. Brand new UFH and insulated screed floors being installed phase by phase and new ASHP installed already, new high spec double glazing along with 10kwp array of Solar and 16kw of Sigenergy batteries with a 10kw SP inverter, new roof with lots of insulation. We are on Octopus Cosy, so have only to last 6 hours at a time before we can recharge the batteries at cheap rate. Plumbing and HW cylinder are all in the unheated basement which is typically around 4-5C warmer than outside temperature. All pipes are lagged, not brilliantly but its half decent now I have improved it. The problem is the Grant ASHP are not comissioned yet and can't be until the whole project is completed as they are specced to run 100% of the house, and not the 45% which is currently completed. So other than for a handful of params which I have adjusted after reading info here and speaking to my plumber, all params are as per defaults. The two ASHP are allegedly configured in a master / slave setup and to date I have only ever seen the slave kick in to defrost itself, never actually running the compressor otherwise. My plumber is very helpful but he isnt an expert on the Grant setup, his plan was also to pay the Grant installed to comission it correctly once the house was completed, but I never realised that would mean we had to live in the interim phases with default settings that may not get the best out of the systems. The ASHP heated the hot water just fine, two sessions a day for about 2hours each and the water was piping hot to our satisfaction for the first few months. No issues with energy use either. Once the main living space was tiled we began to warm it up slowly over a 3 week period for occupation next week. We were struggling to get that room (95sqm) warm enough at first, and have been systematically making one change at a time and giving it a couple of days to settle in to see the impact. A week ago I worked out that the volumiser tanks were not working at all as the default settings leave them disabled. I added the params in the volumiser tank manual and saw an immediate change on the two controllers and an initial hour or so of a huge use of electricity whilst they warmed up. The ASHP seem to be rated at around 2.5kw input whereas the tanks are 3kw each, so bizzarely the tanks can draw more power than the actual ASHP's! We then made other changes. most noticeably increasing the flow rates in the manifolds which have raised the room temp upto 19.5C which is liveable. The issue is that ever since I turned on the volumisers the 16kw batteries no longer last the 6 hour window whereas before enabling them they never ran out. Every single time the compressor becomes active on the master ASHP the flame icon lights up, plus whenever the slave goes into defrost its flame icon also lights up. Watching the live use on the Sig app its clear the spikes in power when the ASHP kick in is significantly higher, I was rarely seeing more than 2-2.5 kw for the ASHP, now I see anywhere upto 8 kw for the ASHP, which understandable chews through the batteries before the 6 hour window expires. I have this morning given in and disabled both volumisers again to try save energy as I didn't feel they had actually helped warm the room up, simply ate electricity. It was mostly down to the flow rate being too low for the room loop sizes. Page 15 of the Volumiser manual says Param 46-00 to 3=supplementary mode (on) or 0=disable, ALSO, Param 51-48 Terminal 46 setting 0=DHW Heater (off) and 1=Backup Heater seem to enable and disable them, most noticeably 51-48 which has an instant response and the "flame" icon appears or disappears on each controller. The main Grant manual makes no mention of the flame icon, so I can only assume it means "volumiser active". I changed all of the params suggested on page 15, but these two seemed to activate them. Id be more than happy to post the small handful of settings ive changed, but largely they relate to hot water temp and defrost settings. Weather compensation is ON and running entirely on default settings. My aim is simply to be able to heat this room plus the main bedroom and ensuite (together which are "phase 1") within the 16kw battery cycle plus the hot water. Ultimately it should be able to do that, other than I accept we may need to add a 3rd 8kw Sig battery once the later phases are completed. Please can somebody help with how to enable the volumisers so they dont eat lots of power, AND / OR any other critical changes we should make either alone or in conjunction with the params in the volumiser manual. Thank you in advance. Adam

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JamesPa

(@jamespa)

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Joined: 3 years ago

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17/02/2025 8:37 am

Posted by: @adam

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So I guess in my head I wanted to get them working given I paid to have them connected up and thus I’ve been thinking they needed to act out their full capabilities.

Thats the only logical explanation because for their main function they emphatically dont.

Posted by: @adam

↑

Perhaps though he never intended them to be immersion heaters simply add volume as you say.

Could be, then once he had received them he realised they had an extra function and thought that it would be best to enable it!

Posted by: @adam

↑

maybe the answer is simply then to leave their immersion heater aspect disabled permanently and just accept they are inactive volumisers. Could possibly even throw the power supply off to each of them to make sure of it!

It definitely is an option. You can always put them on if something bad happens and you need them, at this point you wont mind paying the price.

One more matter - You asked about the water pump mode for the heat pump. On reflection Im not sure how effective sniffing mode will be given that both your heating loops can shut off completely. You may need to experiment and watch.

Another angle just occurred, given your heating loops can shut off completely, its just possible (although unlikely) that the only water available from a defrost cycle is the water in the volumiser. In this case its also just possible (although unlikely) that the immersion heaters may be needed to complete defrost. This is a situation you probably want to avoid.

This post was modified 10 months ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Transparent

(@transparent)

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Posts: 2799

18/02/2025 2:15 pm

Posted by: @adam

↑

in the event of a power failure nothing will work, I know that.

I'm puzzled by that.

The Sig Energy datasheet indicates that there are two separate 240v power outputs.
The one marked "Backup" suggests that it should remain live during an outage.

You'll need to check with your electrician how he's utilised those two ports.

Save energy... recycle electrons!

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adam

(@adam)

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Joined: 10 months ago

Posts: 22

Topic starter 18/02/2025 4:03 pm

@transparent

the backup ports are for use with the optional gateway device which is for just that. I specifically checked. Gateway is extra as was labour to connect it.

We decided we didn’t need that functionality for the extra cost.

it can always be added in later albeit more labour to add it in afterwards.

👍

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bretix

(@bretix)

Estimable Member Member

Joined: 3 years ago

Posts: 85

17/10/2025 10:20 pm

@adam Hi just jumped on this thread as I too have 2 10kw grant aerona 3 pumps and couldn't figure why only 1 pump seems to ever work (never got my head around why as 1 is set up for DHW and heat and the other just for heating), where my set up differs is that the installers put in a low loss header - no volumisers though.

Anway similar situation in that I was on single phase not realising what transparent mentioned about the draw on electricity but have had no issues (from what I can gather it's never used more than 4kwh). The EV charger can take up to 7kwh but never does from the battery management.

With some of these issues inmind I applied for 3 phase and gratefully had free installation from my DNO.... Which opened up another Pandora's box 🙄

I've just started running my pumps again in earnest following installation of a couple of magnacleans going to the pump after having a p1 fault and having to replace after finding sludge and filings.

I'm just about to put some more biocide and inhibitor in following a flush and hopefully should have a more efficient system but already looking at reducing the flow further as it running warmer with the milder weather at the moment.

Did you ever get your system running to your requirements?

2 10kw Grant Aerona3
Heat loss calc 16.5 kw @ -2.8 degrees
4.32 PV

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Grantmethestrength

(@grantmethestrength)

Reputable Member Member

Joined: 11 months ago

Posts: 174

18/10/2025 9:45 pm

The Grant Aerona3 external volumisers are insulated units designed to be installed as per the photos. They have a 3kW immersion heater in them, my installer didn’t wire ours up and we haven’t needed them I am keen to understand why we would need them. I don’t know if you would need them with two 10kW heat pumps that seems like a heck of a lot of heating.

Kind Regards
Si
——————————————————————————
Grant Aerona3 13kW
13 x 435w + 13x 480w Solar Panels
Sigenergy 10kW Inverter
16kW Sigenstor battery

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