Bubbling air sound at pump - tried everything. At a loss...

[drabux]

Hi,
I'm new here but not to DIY. Hopefully in future I can help others with my knowledge but now, I need your help.

So, I have an open vented system with newish cast iron rads and suprima boiler. Ever since I've lived in the flat (3 years) I've had the following problem:

1. Pump circulates water when cold and no bubbling at the pump
2. As the boiler heats up there is an increased intensity of noise at the pump from air rushing by.

What I have tried:
1. Blocked off the overflow pipe in case air entering the system here. Makes no difference.
2. Run the pump without the boiler to see if air being sucked in somewhere. It is not.
3. Suspect sludge/magnetite. Flush the system and use Fernox DS40. No difference.
5. Fit Fernox TF1 to collect magnitite. No difference.
4. Remove every radiator and wash out with hose. Quite a bit of magnitite but no difference.
5. Remove HEX and flush out. Lots of magnetite. Boiler quieter but still bubbling at the circulation pump when hot.
6. Drain down, water looks clean.
7. Remove HEX and clean with hydrochloric acid. HEX now looks clean and flushes absolutely clean. Still no bl**dy difference.

Circulation is fine - all rads get warm, top to bottom.

I'm really at a loss about this and it is driving me absolutely mad. Help much appreciated.
Thanks,
Alan

 

[TCCHeating]

Can you post a picture of the pump and piping configuration nearby? (Including where the feed and vent pipes connect to the system)

If you have a cylinder cupboard it's normally all in there. Without a pic its hard to give specific advice

 

[drabux]

Thanks. I will take a picture and post tomorrow. There is very little head on the system because I live in a flat. However, as I said, I have run the pump for hours without the boiler running and there is no noise (no air being sucked in) and so I have come to the conclusion that the boiler is responsible.

Thanks.
Alan

 

[jeff the gasman]

The low system head could be the problem. This combined with excessive boiler temperature.
Also magnetite build up in pipework around the cold feed and open vent.
You can check for this with a magnet.
Pressurising the system would help if no magnetite is found.

 

[drabux]

Here's the picture of the layout. I'm still not convinced the low head could be the problem since I don't see why air would only be drawn in when the boiler is running (I've had the pump running with and without the boiler on and I only get bubbles with the boiler running)

Pipes

• drabux
• 2 Mar 2014
• 1

I can't seem to get the picture to appear any bigger, sorry.

Alan