Hello again all,well as an update to my origional posts i've had the system powerflushed but made little differance.i've still got a problem(or not) in that the boiler runs for abuout 8 to 10 mins then cuts out,i've noticed that when the boiler cuts out turning the room stat up further has no effect,but turning the cylinder stat up fires it up straight away.I've changed the room stat again today and checked the 3 way (installed last month with pump) and all appears to operate correctly.Question is should i still get live feed to cylinder stat and HW call when heating only is selected on the controller,also it was mentioned to me about Heat transfer paste on the boiler stat thermister-this is dry in its vial-will this have any effect on the problem i'm getting?-could it be the boiler stat itself playing up as it controls the gas valve??-any way of testing this please??