Shower cartridge for "high pressure" or "combi boilers"

[WaterTight]

3 options for a cart I need (haven't taken it out to examine.) Low pressure, high pressure or combi.

They've got a combi, so presumably I'd go for the latter option but what system are they calling high pressure? I thought a combi was 'high' pressure, so to speak. Is Unvented 'higher' pressure or are they talking about some commerical application?

Thanks

 

[WaterTight]

It's Aqualisa, if that helps

 

[Harvest Fields]

Could high pressure mean power pump?

 

[WaterTight]

Dunno. I bought the combi one in the end..

 

[ShaunCorbs]

High pressure and combi should be the same but spec will be listed

 

[JCplumb]

I've done a few of them, low pressure for gravity, combi for everything else, pink one I think it is for combis and grey for gravity.
Last one I did, I swapped grey out for a pink one because they had gravity when the shower was installed - 10 years later upgraded to a combi and the grey cartridge lasted another 5 years with a combi feeding it so I doubt it even matters that much.

 

[chris watkins]

Come on Guy's & girls - it is not just about the pressure, it's the flow rate as well.
Gravity = larger water ways so better flow from a low pressure system
Combi = small water ways with flow range limited so that a hot water being generated instantaneously will get up to temperature, can handle hight pressure.
High pressure = high flow rates & pressure such as you would achieve from an unvented mains fed system or pumped.