Saturday hours by appointment! It is always good practice to ask your heating engineer what size boiler he or she thinks best fits your requirements. Call us today for all your cooling needs! The e-tec range features a brand new stainless steel heat exchanger and is our smallest combi yet. Making sure pipes have proper slope and the job is done right! Our entire combi boiler range is rated energy efficiency class: a. We provide boiler installation, service and repair quotes across the.