I had a Aqualisa digital pumped shower prior to having the ASHP installed’. It had to be stripped out because the ASHP system is a closed mains pressure system and consequently cannot have a pumped/power shower.  Swapped it for a non pumped shower. 

Did you swap it for a another digital unit and is it working ok?

Surely you could keep a vented DHW cylinder and existing cold water tanks.  Also, why can't the ASHP primaries have a header tank like my gas central heating system?

That may be possible, I don,t know but why would you want the worst of both worlds?  poor hot water pressure to taps & showers especially upstairs with a big imbalance between mains pressure cold and gravity fed hot and a pair of tanks sitting in the attic, when you can have high pressure hot & cold supply and a large tank of stored water?

@morgan

Hi Did you swap it for a another digital unit and is it working ok?

@somerpark Mains water pressure isn’t necessarily high pressure. Minimum service level is around 1 bar. It may not be the case that there is a large pressure imbalance between hot and cold supplies.  A pumped thermostatic shower overcomes these issues and it is likely that it would be incompatible with an unvented cylinder. 

@ianmk13 I though mains pressure of 1 bar and above was considered high pressure. and I have been using a pumped digital shower because I have a vented DHW cylinder at present with the associated cold tank and CH header tank in the attic. The pump only overcomes the issue with the shower, my upstairs bathroom hot tap has a 2 metre head, 0.2 bar and my cold tap is mains pressure in my case about 1.5 bar. The heat pump as far as I know only works with an unvented cylinder at mains pressure so it is not an option to stick with my current setup which I would not choose for my situation if it was possible. So the pumped shower has to go.

Posted by: @somerpark

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@morgan

Hi Did you swap it for a another digital unit and is it working ok?

 

@somerpark

No. I swapped it for a non-digital, unpumped shower, and the cold water storage tank was removed. A power shower is not compatible with an unvented closed system. (As explained by my installer.)

Posted by: @ianmk13

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Surely you could keep a vented DHW cylinder and existing cold water tanks.  Also, why can't the ASHP primaries have a header tank like my gas central heating system?

@ianmk13 

How will you heat the water in the retained vented DHW cylinder?  Because you won't be using the ASHP.

@morgan  Why not?  There’s hydraulic separation between the ASHP flow and the domestic hot water.

@morgan It won't be retained, new unvented cylinder with the new ashp all old tanks removed with old gas boiler