Drained down old system, re-filled it - now rads stone cold

[Havago]

I'm working on an old central heating system. The boiler is a floor standing Glow Worm with a Grundfoss pump inside it. It's a bungalow with only one storey and an attic. The boiler and the airing cupboard with the HW cylinder in it are both at ground floor level. All the rads are at ground floor level. The cold water storage cistern and the F&E tank are in the attic.

I drained down the system so that I could remove a radiator. When I filled the system back up, I found that only one radiator is now getting hot. This one hot rad is next to the boiler. The pipes to it tee off directly from the flow and return pipes to the boiler (see diagram).

Apart from this rad, all the radiators are drop-fed from the attic. So the pipework goes from the boiler, up through the ceiling, into the attic, then drops down into the various rooms to feed the rads. All of these rads are now cold and will not heat up. Even the pipes going to all the other rads are totally cold.

The hot water cylinder is still getting hot. So the customer still has hot water.

The flow and return pipes from the boiler to the heating system are hot where they come out of/go into the boiler (I think). As previously mentioned, they tee off to the hot rad and that rad is very hot. But when I felt these flow and return pipes as they ran up to the attic, they became less warm. Both were still noticeably warm however. But when they go through the ceiling and into the attic, they appear in the attic and they are cold there! I checked and they were definitely the same pipes (my colleague wiggled them and I could see them moving on the ground floor).

The only things I can think of are either an airlock, or the pump is not pumping hard enough. I bled all the rads a few times but no air came out after the first bleeding - only water. I also bled the Grundfoss pump. Some water came out there too so I assume no air trapped there. I took the cover off the pump and checked that it was spinning. It was. I assume the pump is working because it's spinning and because the hot water is still getting hot and the one rad is getting hot. But maybe the pump isn't pumping hard enough to get the water up into the attic? Or, maybe there's an airlock at the point where those flow and return pipes go into the attic? On the side of the pump there was a little black switch, but I couldn't see what the switch said on it (out of view) - it seemed to have 2 or 3 positions though.

I tried the trick with putting a hosepipe into the F&E tank, with one end on the cold mains and the other going into the F&E draw-off pipe. I put loads of water in there and it was coming out of the vent pipe. It was sometimes hot coming out of the vent pipe. I tried to put my hand over the vent pipe as I was doing this to create more pressure in the system (to try to get rid of any airlock) but this was difficult as I could barely reach my hand to the vent (very limited space) and sometimes the water coming out was hot.

I thought of putting some de-scaler in the system but not sure that it will even pump round if I do.

Any ideas anyone?!
Thanks in advance.

 

[tomy]

check for any bleed valves in the loft along the pipework , just cause the rads are full of water doesnt mean there isnt air trapped in one of the pipes.

 

[Garfeild]

Try stopping and starting the pump,also what ive done before in similar circumstances,is to put a hose on a drain off on one of the rads fed by the up and over pipework,stick the hose out the door,open the drain off fully,and let the water run out,hopefully the air will be forced out with it,you could try the hose on the expasion tank outlet in conjunction with this.

 

[Havago]

Thank you so much for your suggestions. Tomy, I think you might be right - there were some little thingies at the top of those pipes, which I now think were air bleed-off points. How do I bleed off the air from one of these - just turn it with a spanner/ rad key?
Garfield, I will also try what you suggest. Do you think it's OK to turn the pump on and off at the socket? I don't know how else I can do it because the switch at the side of the pump doesn't seem to turn the pump off - possibly just varies the speed.

 

[stardanny]

Switch off heating system and go up in loft and open air bleed point till water come out, there should be two bleed point, one on flow and another on return, you may need to do again if below didn't work.

When done, switch heating on and if one or a few rad get hot, other still cold, turn off hot rads ( on rad valve or trv if fitted, do not touch Lsv ) pump will force heating water onto cold rads, clearing out air, keep doing that till last rad get hot, finally open all rads valve, bleed any remaining air out of rads.

Dan.