Air In System

[gx600]

I have a conventional CH system. CF boiler with 8 rads and gravity fed hot water tank which has worked problem free for many years. Last week I heard loud noises from my pump which appeared to sound like air in the system. I checked the rads and found 3 with a lot of air in. I have checked throughout for leaks but can't find any. If I bleed the radiators the pump continues to make the noise and in a short time they are full of air again. I checked the header tank and found the water in it warm and murky. The outlet pipe (ch feed) from the tank is warm and the overflow seems as though it could have passed water (wet in the pipe).
Any advice appreciated.

 

[Bahco]

Try bleeding the pump. Do a saerch on this forum

 

[gx600]

Thanks for the reply but theres a bit more to it than that. We are talking about a system that I fiited myself 17 years ago without any faults since. Its now getting large amounts of air in very quick time. The faults seem to indicate some sort of sludge blockage but what doesn't make sense is that if I isolate half of the system the problem halves.

 

[brumylad]

check for a blockage were the cold feed meets the main pipework. Do this using a maget, it will stick if the pipe is full of iron sludge.

Also could try holding a glass of water under the outlet of the vent pipe, it shouldn't discharge or suck up any water. Put on a rubber glove if you do this so you don't get burnt.

 

[gx600]

Thanks. I will give that a go tonight.