Clearances
The boiler should be positioned so that at least the minimum operational and servicing clearances are provided, see your owner's manual. If you haven't got one, try here:
http://www.gotoplumbing.co.uk/findamanual_results.asp?pageSize=25&accid=993&sortby=&catid=3146&pg=4
Additional clearances may be required around the boiler for installation purposes.
I have a glow worm 100e compact fitted in a larder cupboard, hides it fine, but, gives the serviceman grief when it needs repairing! The minimum clearance each side was 5mm, but at least 150mm below & 25 ABOVE THE TOP OF THE BOILER CASE OR THE FLUE ELBOW IF FITTED. Hope that helps, oh, & make sure your fitter is corgi registered for safety & insurance puposes!
Chris Wiles, January 2009