I know that this post is a old one.. just to give some information I am replying to this post.
There are many website available online. Search for the boiler name in google and you can get may result. Just choice the cheapest one avaiable. Google has recently launch a new search engine for products. Its called Google Shopping (Google Products). Try this new search engine. The link is http://www.google.co.uk/prdhp?client=firefox-a&rls=org.mozilla:en-GB:official&hl=en&tab=wf .. This can help.
Finally I want to suggest you to go for plumb traders. They sell all the different type of boiler avaibale in the market.
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