Gurgling boiler

3 Jan 2008
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United Kingdom
Hi all,

I have an open vented pumped system, the boiler and HW cylinder were installed october 2009.
I have recently drained down my system and replaced a radiator as the old one had seen better days.

I have refilled and bled the system, no more air seems to be in the system.
However when I turn the heating on either by the programmer or when the stat calls for heat I get gurgling noises from the boiler, like water is being poured down the pipes to the boiler. But only for the first 5 or 10 seconds then it stops. When you turn the boiler off you hear another noise which sounds like a bubble of air going back up the pipe from the boiler.

I thought it may still be air, so I have had the system on and bled several times and occasionally get a very small amount of air out of the bathroom rad upstairs.
The noise is still there. I checked the expansion tank in the loft and this has water in it. I did notice that when the boiler is switched off the pump stops but about a cup full of water gets pushed up the vent pipe and in to the F & E tank. Is this normal?

The boiler makes these noises evertime it is switched on and off.

I don't know what else to try. Appolgies for the long post.
Any ideas appreciated.
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No apologies neccessary for the length of your post, more relevant detail aids diagnosis significantly. I've never had any complaints about the length of my post!!

The cup full of water is called pumping over, and is bad because it oxygenates the water and leads to rapid corrosion of the steel parts of your system. The cause of the pumping over may be to do with the recent work. Others may be able to help with online photo links and diagrams to help eliminate it; I'm not 'puter literate enough. Suffice to say the cold feed from the header tank, and the open vent pipe should be on the suction side of the pump, no further than 150mm apart. Generally the pump will pump the water away from the flow side of the boiler in an open vented installation.

Is there a facility to expel air from the high points near to the HW cylinder? That could be why you get persistant gurgling.

Thanks MM.
I may have to try and post a couple of pictures. But the feed goes in to the top of the pump, with the pump flow away from the feed. The vent runs right next to the feed, I would say no more than 100mm apart.
These two pipes are joint just above the pump. Therefore from your discription, this seems correct.

There is a manual vent near the HW cylinder, attached between the 3 port valve and the connection to the the cylinder about half way up the cylinder on and extended pipe. I have tried but no air comes out only water.

I also have a vent on top of the magnaclean which is next in flow after the pump. again no air is released.

As I say I don't know what else to try. :confused:
A photo of the pump area would be useful.

It seems you have the pump pumping downwards, do you have a vent at the high point on the suction side of the pump. My interpretation is that the fill and vent connections are horizontal, teed into the vertical pump suction pipe.

Does the open vent pipe have the ability to vent ALL of the air from the suction side? Does it rise CONTINUALLY between its connection and the area above the F&E tank? Could an air pocket be formed or does all air that enters tha vent pipe get vented?

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I will take a picture and post tonight.
the pump is indeed pumping downwards. But both the vent and feed run vertically up from the pump area.

The vent pipe does rise continually up to above the F&E tank. I cannot see anywhere where air could get trapped in the vent pipe.

I do not have a vent above the pump, other than the vent pipe obviously. I am trying to explain it the best I can but will post a picture later will hopefully will help.

One thing I have just thought of is would it matter how full the tank is. I have never adjusted the ball cock. But reading through the FAQ section on here says the water should be 4 inches high when cold. I would guess I have more like double that. Would it make any difference?
ok, i have been having more of a look at this. Here is a picture of the pump arrangement.
the right hand pipe is the feed and the left the vent.
This is the arrangement lower down.

I have now managed to stop it pumping over. The vent pipe looked to be going downwards towards the tank. I found if i moved the pipe up slightly it didn't pump over.
This then stopped most of the gurgling and now i just get a slight water running noise when the pump first comes on. almost like someone is pouring water down the pipe leading to the boiler.
All i'm wondering now if I am just masking the problem and there is still a problem somewhere. The boiler is a Potterton Promax 15 SL if that makes any difference.
If anyone could put my mind at rest I would appreciate it.

Many thanks
Check around the H section with a magnet and see if it is attracted to the copper. H section is exactly that, the pipework just above the pump, cold feed and vent etc.
Just checked the H section with a fridge magnet. Its all i could find quickly. It would not stick or attract to anything in that area.
I presume this is a good sign?
thanks. I needed that. :)
Is the trickling water for a few seconds when the boiler turns on normal?
does anyone know? Everything seems to work, i'm getting hot water and hot rads and now its not pumping over.

Just hope i'm not masking another problem.
It sounds like its trickling in to the boiler for about 5 seconds after the boiler switches on and then goes away, then will only do it again when it switches back on again.
Thats what i thought. any ideas how to get rid of it please. Or will it go of its own accord as obviously i have drained the system down to fit the rad.

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