Have Gazco responded to you?
I have just had a Gazco Studio Slimline fitted at the start of April and I have 3 major problems with it. I notified my fitter over a week and a half ago when the problems started and they notified Gazco who have so far not responded with a solution.
We have used this fireplace less than ten times: the wall is cracked above the large frame we were advised to choose to hide potential small cracks due to the heat output, the fireplace previously switched itself off after 5-10 seconds (this was intermittent at first but one night we had to 8-10 times before it would stay lit) and now it won't even switch on. It has a new brick effect back panel as the other one cracked after being fitted and this now has a large soot line near the right corner after only being used twice.
I am really concerned after reading these posts and this cost a lot of money plus after less than one month in, there are serious problems.