Baxi Duotec GA

I bought a Baxi duotec ga24 two years ago and assumed it had the same guarantee as other duo tec combis ie 7yrs. It broke down with a pcb failure after two yrs and two weeks. I contacted Baxi who said tough but that make has only two yrs guarantee on it.It worked fine till that happened. I have been informed that this is because it is an inferior model so was given only a two yr guarantee. I do not feel that I have been sold this model in good faith by Baxi and would think that a reputable firm would help me on this. they should have told me about the problem.