Join our mailing list to stay up to date for our newest coupons and specials. You don't have to use your energy provider's boiler cover! Fired boiler / hrsg, sizes up to hp. The fire tube design of the heat exchanger provides a greater efficiency and a lower pressure drop the built in stainless steel indirect storage tank provides endless hot water and eliminates temperature fluctuation! Boiler & central heating cover deluxe. The expansion vessel (right) is normally installed.