single pipe system pipework blocked ? System is 7 rad single pipe in a bungalow fed by Worcester combi boiler. After many years of being hottest house on earth rads are struggling. Service engs [ same ones for many years] have changed pump , cleaned with sentinel 800 [ though i don't believe it was carried out correctly with regard to correct flushing / draining ] They believe the pipework is fouled and have recommended a full system pwk change to a 2 pipe system , obviously at considerable cost. The system is in my mother's house but I've spent some time there and carried out following trials.******..Left system running with a single rad on line for 30 mins , repeated for each rad in the house. Every rad heated up fully. To me this means there is some sort of route thru all the system pipework. The engineers have agreed to carry out a further wash at reduced cost but following job method that I have supplied them from both Sentinel and Fernox , may use a fernox product this time.*********...Any thoughts ?