Unvented cylinder or not?

[stiz]

My hot water pressure is really bad although I have good cold water pressure. The house has been extended a little and I also want to add another shower.

I currently have a gravity fed system with the cylinder in airing cupboard and most water pipes 15mm and to radiators 12mm. I have a Potterton boiler that British Gas (and the plumbers I have spoken with) say is definitely up to the job.

I thought the best solution would be to put in an unvented system in - I niaively thought a plumber could take out the old cylinder and put an unvented one in its place, making minor adjustments to the pipes so that they join up and using the existing fused power supply.

However, I have spoken to 2 plumbers who both have told me to raise the height of my cold water tank by 1/2 metre and fit pumps on the showers to solve the problem. They claim that if I want to go for a new cylinder then the house will need extensive replumbing using 22mm for water and 15mm for radiators. They don't seem keen to do it.

The only quote I've had is for £1500 labour plus parts.

Is the advice I have been given right and if not, what should I look to pay for an unvented cylinder to be fitted. (I'm just outside Coventry and as the price of cylinders varies so much assume I am supplying this myself - but the Santon PP210B is my favourite at the moment).

I know this is not a DIY job so is there anyone out there that would be interested in giving me a quote???

All comments would be gratefully received! Many thanks.

[bobplum]

for cost and hassle purposes i would install a pump cost around £150 for a good one depending on the layoiut of the house a days labour say £200