I've got a problem which has recently developed with the header tank. The updated system (replacement boiler, pipe rerouting) has been in for about 10 years, but some of the radiators are older. The system has been ok until recently but a year ago I decided to replace 2 v. old radiators which just happened to coincide with a blocked pump. No obvious problems with the system and the header tank seemed ok. Pump replaced, new radiators fitted, system flushed, inhibitor added - all working well. Despite that the water inlet has become blocked twice by sludge and has been getting brown/orange water in the header tank together with some scum. Power-flushed the sytem with cleaner - added inhibitor. Again the header tank is starting to collect brown/orange water and a layer of scum. There are no evident leaks in the system - no build up of gas in the radiators. It all runs ok - except that sludge is probably going to build up and block the water inlet again at an inconvenient time and I'd guess there's something else wrong to cause the dirty header tank.
Any suggestions which don't involve ripping it all out?