I don't have a practical bone in my body, so I'm not complaining about the level of DIY knowledge of Him Indoors, but we have a couple of questions about the Truma Combi Boiler please. He can't find the answer in the handbook - it's probably too basic a question, they'll think everybody knows.... He's drained the main tank with all of the mixer taps open & turned to the 'hot' end. 1] will this have drained the boiler tank? 2] if it has, can we use the blown-air heater, or does this need the boiler (and/or main tank) to be filled? Thanks in advance!