ALVA GAS/ELECTRIC HEATER - GH309

I am disappointed that I can't give this company a zero rating, because the Warranty that I still have on the purchase of my Alva Heater, has been considered as Null and Void, after their inspection to this unit. Their reasons happen to be because I have used a 7Kg. gas cylinder instead of a 9Kg. In fact, their instructions booklet recommend a 9Kg. gas cylinder for this particular heater but, my question is: What difference does it make by using a smaller cylinder? It makes me think that such particular recommendation on their instructions, only serves the purpose to render your Warranty as Null and Void, when you don't follow strictly their instructions booklet. As a matter fact, I have used the same 7kg cylinder on another Heater that I borrowed while mine was being inspected by them, and everything worked perfectly. Thus, where do I stand? Am I entrusted to give up on any further attempts to save such still valid Warranty!!!? I need help and a good and reasonable advice. My e.mail address is: ***

NOTE: I have also written a review on their site.