Hi guys, In the past 18 months I have had to replace 6 radiators (out of 12 in my house) due to pinhole leaks. The first 3 developed leaks on the ball by the lockshield end. On the last 3 the coating bubbled between half way up and near the top of the rads. The latest rad to go is a designer rad that I installed only a year ago! The others I believe were installed when the house was built (around 20 years ago). On most replacements I drained down the whole system so I could replace the old TRVs for new ones at the same time, each time I added inhibitor when filling the system again. On the last drain down I filled up with a cleaner for 5 days, drained down and filled up again with inhibitor. I thought I had loads of sludge because rads were only getting hot up the sides and top but I beleive my system isn't balanced properly because they all get uniformly very hot when I turn all the other rads off. Don't think it's related but for as long as I remember the HW & CH both have to be on the control panel for the rads to come on (I think it's the 3 port valve). My heating system has a light banging through the pipes when it's on, more when it first comes on then subdues after 30ish mins which started a couple of years ago. Last night I discovered this (see pic) in my airing cupboard and wondered if I'm on the brink of a disaster and if its connected? I am not a professional plumber but competent enough to tackle most jobs. I just want to stop replacing rads!!