My central heating system was installed in our brand new house 5 years ago. I have a Suprima 50 boiler (already encountered the lockout/pcb problems) running the hot water and 12 radiators in the house.
After about a year, I was getting severe boiler kettling and lots of bubbling radiators/air trapped in radiators, particularly in the winter when the system gets hot with lots of use. I suspected that the builders didn't add any inhibitor when they commissioned the system so I've tried all the treatments below. But the kettling and air always return after 6-9 months.
1. Added Fernox boiler noise reducer. Worked for a few months but problem returned.
2. Flushed entire system and added DS-40 into entire system as per instructions, then added X100 inhibitor afterwards. Problem cured for about 18 months.
3. Suspecting a leak (because only fresh water introduced would make the limescale constantly build up?), I drained the system and put some leak sealer in. Then added another dose of X100.
4. Added X200 de-kettler and X100 inhibitor and left in system. Kettling and air returned 9 months later.
Each time the problem returns, I have to bleed the air from the radiators and the air expelled smells of what I can only describe as "metallic". The water in the radiators and header feed tank is always dirty rusty brown with clumps of light brown/beige "gunk" floating on top.
5. Last weekend, with the circuit closed to just the boiler, hot water tank and 1 radiator, I drained the brown water and flushed the closed circuit several times with clean water. I then added DS-40 to de-scale the boiler. There's lots of bubbling going on when the pump is running but I believe that's the DS-40 doing it's job. Already the water in the header tank is brown (but no gunk yet).
Before I go through another cycle of adding X100 and X200, I wondered if there was anyone who might have some advice of something else to try.
My questions are ...
1) Why does the radiator water turn brown and smelly despite the X100 inhibitor ?
2) How can the kettling return so severely despite the X200 remaining the in system?
3) What's the slimy gunk that appears in the header feed tank ?? Is it normal ??
4) Am I missing something, here ??
5) HOW CAN I STOP THIS ENDLESS CYCLE OF HAVING TO DE-KETTLE THE SYSTEM EVERY 9-12 months !?!?
All advice gratefully received (apart from move house, install a new system etc.