they do have a water throttle on the side of the brass water section which can be adjusted to just slow the water and allow to heat. not the kind of thing that would fault though so cos of the half flame size problem i would say possibly more to do with the diaphragm maybe pin holed and allowing less differential pressure and not lifting gas valve open properly.
you can get a replacement diaphragm for the water section but get the o-rings too or you'll never stop the leak after you re-assemble it. trust me.
iain
May 2008
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