isolate boiler, go in to loft locate the small plastic tank,if fitted with mains isolation turn off, if not surport ball valve with a length of string or wire, locate a drain tap on one of your lowest rads connect a hose open valve and drain. give 5 mins open an upstairs bleed valve on rad to let air,that will help fully drain system. should be fully drained within 15mins.
hi-spec plumbing, January 2007
