Radiator needs bleeding

[Kazal]

We have 1 radiator that needs bleeding every other day. The top 2 inches are luke warm until I bleed it. Why is this as I thought that the systems were sealed and should only need bleeding a couple of times a year.

[buildersmate]

Sealed systems scarsely ever need bleeding - let alone 2x per year.
This is 95% likely to be caused by corrosion that is slowly eating away at the steel radiators in your system. Have you got corrosion inhibitor in it?
Without it, water in the system eats away at the inside surface of the steel radiator, producing magnetite (a black sludge, oxide of iron) and hydrogen gas. It is the hydrogen gas that collects at the top of your rad.
Over many years (10-15), the rads will rust through from the inside.
Over a shorter period of time, the sludge will collect at the bottom of the rads and prevent the proper flow of water in the system.
Suggest you have inhibitor added. If a bad case, the system requires flushing first to remove any sludge already formed.

[Kazal]

Thanks for this, but all the radiators have been replaced over the last 3 years and we had the system power flushed and the header tank cleaned out last year by a reputableheating firm so I would hope they replced the inhibitor. How can I check?

[zzxxee]

mmmmmmm tricky one this i wonder if your household insurance will cover this sounds like you need a plumber

[colin6789]

Is the system pressure OK, there should be a pressure gauge on the boiler, if you bleed the system the pressure will go down. there should be a hose with a valve by the boiler to put more cold water in to put up the pressure. If the pressure if low the pump may suck in air as it is below the outside pressure (a slight vacuum) it may not leak water out at higher pressure.

[Brooksy]

I had a similar problem year before last in a 10 yr old system. Turned out to be that the little plastic tank (I don`t recall what its called) in the loft, close to the big one, had a stuck ballc**k arm. The ball float was sitting in mid air because of corrosion at the pivot joint. A clean up & some oil then grease & it`s been good as gold. I think it`s called the expansion tank, & it maintains the radiator levels.