Noise in Airing cupboard

[mystic]

I'll aplologise now just incase I have missed a topic about this.

A few months ago we had this banging noise in our airing cupboard. We had a friend of ours come round to inspect it (he works for scottish gas) who said it sounds like the pump has gone. We got a new pump and all seemed to be fine until a a few days ago when the banging sound came back. It seemed that the pump had gone again only after two months. The same friend came around yesterday and said the pump is very slow and is struggling, so off hubby goes to get a new pump, one that is well known called Grundfos. The new pump was installed and all seemed well until this morning when the banging noise came back.
Surely there must be some other problem other than the pump. This is the 3rd pump in 3 yrs. Hubby did bleed the radiators to see if maybe that might be the problem but it hasnt made any difference, although with one of the radiators which is in the kitchen there was a lot of air in there but also black liquid came out of it.
When I asked the friend he didnt seem to concerned about it as the water from the pump which had to be changed came out clear. Could this be the cause??
If someone out there knows what the problem could be I would really appreciate your help as I cant keep paying out for new pumps every two months or every year.

 

[COG]

your grundfoss pump should work for years,you must have a system fault that takeing them out, your pump is lubricated by the system water so if you are getting air drawn into the pump it will burn it out, you can usually smell a burnt out pump. pumps can allso stick from magnatite (spelling ?)wich is a black form of sludge that will atatch itself to the hot internal surface of the pump allso if the head of the pump is positiomd wrong the bearings will fail for the correct position look at the instructions with your pumps, if the impellar is black on the second pump undoo the four 4mm allen screws and split the body (tap with a mallot )then look at the large rubber seal just under that is a lip that can be pised up carfully and the entir armeture should come out, if you can get it out you can tell what went wrong. i once followd a brit gas man who fitted 14 pumps before looking for the main problem