mixer tap and sealed CH system

Twaddle: are you sure he said that? You'd need to check that the new valve is definitely one intended for mains pressure but suspect you'd be hard pressed to find one which wasn't.

Sealed systems like yours are ideal for showers - you have mains pressure for both H&C supplies which is far better than what an electric shower will give. Plus you will be using gas- rather than electrically heated water, which for now at least is a lot cheaper.

BTW - when you say 'electric' shower I assume you mean one where the electric heats the water instanteously, rather than just an electric booster pump which provided water already heated by gas?

David

Yes, she wants one of those old fashioned things to replace the instant hot water electric job.. The Vaillant is a combi, but its sounds like this is OK?

Sorry, hadn't realised you were talking about a combi; I thought you meant you had a pressurised HW storage tank, for which it would be a no-brainer to use a mixer valve (hence the 'twaddle' remark!). It's not quite as clear-cut with a combi, although depending on the unit I'd say it would still give you a better shower than an electric one. And although there are certainly suitable mixer valves out there, you'd need a pressure-balancing one specifically intended for a combi.

Google the archives of this group for "combi" and "shower" for more on this.

One other consideration - if your combi were ever to break down, you'd be left with no means of producing hot water (with a hot tank, you'd presumably have an immersion heater); if you were to retain the lecky shower it would at least provide a back-up for washing!

David