I am fighting the same war at present, our bungalow has the radiators on drops from the loft and the boiler is a long way from the header tank with lot of horizontal pipe work in loft between. Long-term we are likely to change to a sealed system, but I don’t trust the current pipes to cope with a higher pressure without some leaks somewhere and too much of the pipe work is boxed in to make it easy to find and fix any leaks the higher pressure reveals.
Firstly next time you have a system drained down, I think it is worth fitting a filter on the return before the boiler to capture any partials in the water, they don’t cost that much and help to product the boiler. A Filter aid chemical (Sentinel X900) make help getting any sledge into the water so the filter can remove it.
I have just fitted a Spirovent Air separator to our system just after the boiler feed. Hot water can hold less air then colder water, the Spirovent Air separator removes a lot of micro-bubbles of air from the hot water, as the water cools in radiators etc it adsorbs a bit of air. If it works as claimed, after a few weeks the system will be fee of all air pockets and remain so. (Standard bleeding still needed when refilling the system)
3. Jewson are hiring power flushing units for about £50 (in the drain cleaning section of the hire website for some reason!), I am planning on using one in a few weeks after the X400 that I am putting in today has had time to work.
