Hi.we have feroli boiler for last 8years.it has given us a lot of trouble.i want to replace it.which is the best brand.Vailent or Vokera.i am more intrested in vailent than vokera.i have asked few instalers about vailent ,they all say they are installing or recomend 28 pro model.i am intrested in higher model number.they all say they only install this model only.what could be the reason.any advise is appriciated.thanks.