I have a Ravensheat condensing boiler 85T (I think), ?

It was installed in August last year and works fine apart from when you put the central heating on, it ignites,then goes out and the only way for it to stay on is to turn on the hot water tap, I cannot get a hold of the person who put our central heating system in, do I get in touch with Ravensheat ( I believe it has a 3 year guarantee).