I have to change an old boiler. Which one should I choose for a open vented system (cold water tank, hot water cylinder, F&E cistern) ? Vailland ecotec 438 or Worcester Bosch regular 30? I heard the vaillant has a lower maintenance cost with cheaper parts. But worcester has difficulties to put hands on because the very limited spaces inside of the box. Is it true? I thought Worcester is the German products and more trustable, is it?