First a profile is not a combi, make sure you are testing the swichted live and not mains feed into boiler. Is your system fully pumped? or is it part gravity system, is the pump running, is the control valve (3 port valve) working? if you do not fully understand how a heating system is wired or how the controls work you would be better off calling in a local corgi plumber probley cost you �30 to �40, better to pay them than to do some damage by messing about with the wireing.