I have replaced a radiator with one which is 80mm shorter. I was sold 2 40mm adapters (15mm piping) but have had problems fitting them without leaking. Any advice? Also my heating & water works entirely on a combi boiler using mains water pressure with no tank. If I have to remove either the stop valve or thermostsat valve, do I need to drain any of my system and if so does this involve more than draining the radiator?