Here are some links to sites you may find useful:

Agacentral.com
Lots of lively disscussion about Aga related subjects from owners and engineers:
http://www.agacentral.com/phpBB3/viewforum.php?f=2&sid=c0601d5dcd4b50af73de5176bf0c0055

Pinnock Brothers
Heating oil supplier in Thatcham who helpfully quote their latest price on their website:
http://www.berkshireheatingoil.co.uk