The Vokera manual says code 03 is due to flue or fan problem. This fits with your symptoms. If the fan is working OK it may be a build up of dirt in the tube/sensor near the fan -- from reading other forums it seems this can easily be cleaned out.
So the (hopefully) good news is that fixing your problem should be relatively easy, quick and cheap. No need to drain water or touch gas.
ChrisABC
February 2010
howtomendit.com for free repair help, information and advice.
