Vaillant 637 ecoTEC Plus System Boiler is a top spec ErP A rated condensing systems boiler from the Vaillant Range with a stainless steel heat exchanger. The ecoTEC system boiler is suitable for use with unvented pressurised systems. Vaillant Boilers are highly efficient and deliver a top SEDBUK Band 'A' rated fuel efficiency and powerful DHW performance. Vaillant are widely recognised as the leading heating technology company in Europe, and as one of the market and technology leaders, Vaillant develop best in class products for domestic comforts.