Central heating system bangs, and a noisy pump

[BigHammo]

My central heating system is about 30 years old , but has had a new boiler, about 7 years ago, It it now having the following problems.

1. The pump sounds like it is pumping gravel. Increase the speed and it gets louder.
2. When the system comes on we get a lot of banging for about 10-20 mins then it calms down and all you can hear is the pump.
3. There are 3 radiators that you can't bleed at all. Ie open the bleed valves and the air hisses for a second, out but no water comes out. Then nothing.
4. Also open the main bleed valve and no water comes out and does not hiss.
5. The other radiators bleed but water doesn't rush out.
6. None of my radiators on the ground floor come on until you turn the pump speed up. But I still get no. 1, 3, 4.
Hot water works.

Boiler is Warwick, pump is a myson unit 3, 6 rads upstairs, 6 downstairs.

Any clues what could be wrong?

 

[picasso]

All points to a blocked cold feed or the ballcock stuck, have a look in the small tank in the loft and see if there is water in it.

 

[BigHammo]

All points to a blocked cold feed or the ballcock stuck, have a look in the small tank in the loft and see if there is water in it.

Thanks for this I have been up the loft and the tank is full of water. The ballcock works ok.

I have 2 bleed valves in the airing cupboard and neither of them have any water in them. So I don't know what Is blocking water getting to either of them there is a T valve (or is it called a Y valve. I am baffled as some radiators are hot and others aren't.

Any. Clues?

 

[picasso]

There should be a 15mm pipe coming from near the bottom of the feed and expansion tank, where this pipe meets the system (usually the 15mm pipe goes into a 22mm pipe ) is where is usually blocks, try using a magnet on the pipework coming down from the loft.

 

[BigHammo]

Thanks I will go and find my magnet

 

[BigHammo]

Thanks I will go and find my magnet

Ive tried that but still no joy. If I put an inhibitor in the tank will that help me. Or will my air lock/ blockage still be there?

 

[picasso]

Too late for inhibitor, try draining some water out of the system and see if the ballcock opens on the feed and expansion tank, then you will know for certain if the feed is blocked.