Plumbing in a Shower Pump in the Airing Cupboard?

I am planning on fitting a 1.5 bar max Showerforce Turbo 2 Shower Pump into the airing cupboard /Hot Press and the space and the way i want to plumb is the easiest way I can find this means placing it before the copper water heater cylinder and not after it .

But I am wondering if I do it this way will it pressurize the copper immersion tank so much that it will cause the water to travel up the expansion pipe to the cold water storage tank in the loft?

To make it easier to understand I have uploaded a diagram here of what I want to do:

http://www.flickr.com/photos/14692679@N0...

or:

http://tinyurl.com/7q8hb3

Thanks.