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

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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

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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.  

Posted by: @adam

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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.

@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.

@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?

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.