CH not working - blockage??

[Toki]

My girlfriends heating has packed up today. The system is gravity fed from a tank in the loft.

When we put the CH heating on via the programmer the boiler fired up for a minute or so and went off. The pump was making a funny noise then. The pipe between the boiler and the pump was really hot but the pipe on the other side of the pump was cold.

I went down to B&Q and got a new pump, fitted it but still have the same problem. It sounds to me like the pump is empty when on (only air - making a funny noise) Ive tried bleeding all the radiators as they seem to fill up with air when the pumps on. Once bled there is very little pressure in them, ie little or no water comes out.

Ive checked the tank in the loft which is fill (a bit dirty) and the ballcock is working. However my guess is the water isnt feeding into the pump for some reason. Does this sound right? What could cause this, a blockage?

Could this be a blockage somewhere around the radiators? Also where is all the water going from the radiators as I have bled the raditors a few times to leave them fill with water.

Any further information required then just ask.

Thanks in advance. Trying to get it working before xmas!

 

[alan m 1974]

GET hose pipe and place over c/feed in tank so its in the hole and then place other end over mains at ballvalve,try forcing it through,if you can get a hose pipe onto a drain off and backfill system venting rads until all full then turn hose off

 

[Toki]

I dont have a hose pipe but Ill get one tomorrow and give this a try thanks.

You mention drain off and backfill system. Does that mean the water in the radiators is draining off and not staying full?

 

[alan m 1974]

No imean find a drain off ,small brass fitting on pipework downstairs or by a radiator,maybe rad valve has drain off built on,it will have a small spiggot type hose connector on it and a small square nut were you can undo it asnd release watern,have a look now

 

[Toki]

I cant see any square fittings im afraid. Radiator has hexagonal fittings on the top where you can bleed the air off.

Are these normally at the bottom of the radiator? Ive checked the pipework I can see, but nothing there either.

 

[leakydave]

You may already have tried bleeding the pump... turn heating off, use large flat-bladed screwdriver to open the large silver screw in line with the pump spindle... open slowly until a) air comes out followed by water, or b)water comes out.

The pump may be working fine but a CH pump is crap at pumping air...