Gurgling system but vent pipe is after pump

[eurodave]

All,

Since the cold weather really kicked in I've been plagued by air being drawn into my system and waking my 2 year up in the morning too early! I've taken up carpets tonight to figure out the exact layout (see below).

A couple of years ago I paid for a new Worcester boiler to be fitted upstairs instead of the old boiler and flue downstairs. I think the plumber cut corners with the vent and cold feed because they are now after the pump. There is also an auto-bleed valve and I think this is upstream of the neutral pressure point, so effectively useless and could draw air in.

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• eurodave
• 21 Nov 2014
• 1

The auto-bleed valve I have never trusted because it leaked once. However do you think this will cause the air to be drawn in, or could it simply be a case of putting more inhibitor in the system instead? It happens without fail every morning despite bleeding every day.

It would be expensive to move the vent and cold feed so I'd like to avoid that - but is it my only real solution?

 

[picasso]

I would look at the possability of sealing the system, if not you are going to have to move the vent.

 

[Gasguru]

Why would it be expensive? It appears the boiler is in the airing cupboard above the cylinder/pump/mid-pos valve. No big deal to run the feed/vent up to the loft.

As it stands the system is not compliant with safety standards and if air is being drawn in due to the the system being largely under negative pressure it is gradually corroding away.

Auto air vents are always problematic and best replaced with manual vents.

You could go for a sealed system but that can have it's own set of problems.

 

[footprints]

I think I would look at a sealed system too, with the boiler level just under the F&E tank you may well have problems even with a correctly piped vent and feed.

 

[eurodave]

Thanks - the reason it may be expensive or not an easy fix is that the boiler sits just below a flat roof, so there's no loft above it to thread pipes through.

Although it sounds like this is certainly what I'm going to have to do somehow.

As for sealed - I'll look into it but I am not convinced the pipework will take the pressure - had to tighten up quite a few compression joints over the years so extra pressure makes me nervous.

Thanks all.

 

[picasso]

Another option is a plate heat exchanger if your boiler is suitable for sealed systems.

plate 2

• picasso
• 22 Nov 2014
• 1

 

[Wongfeifox]

This looks a bit of a mare, I wouldn't worry too much about the auto air vent because at the moment you don't even have a neutral point with that set up. Sometimes they do an effective job, sometimes they leak, Sod's law, but try to keep them off any return pipe work, although I have fitted them there as a last resort in the past, depending on system hydraulics.
Rule of thumb is boiler, open vent, 150mm before cold feed then the pump, this will give you the neutral point. Could you not run a 22mm combined open vent cold back before the pump, or is this going to be costly with the flat roof.
I would have thought this should have shown its head before and not just started his winter, but as a previous commentator has said, this system is sucking in air and will eventually sludge up with some lovely red coloured muck. A simple, but not always 100% effective test is to place a milk bottle with water in, over the open vent pipe in the header tank when the system is running, if water is drawn up the open vent! then you need to address this issue.

 

[eurodave]

I think, after monitoring it further, that the gurgling is on switching from hw + ch to just ch. I presume this leads to a sudden surge in pressure as all water is diverted through the radiators. Could it also be that when it is ch + hw that the hw circuit being low resistance takes most of the water? Should I look to somehow control this distribution / balancing even when the vent position is fixed?

Can anyone tell me where the neutral point is on the system?

Could I extend the vent and feed back to before the pump under the floorboards or are there regulations regarding this - it will be a large horizontal run.

Thanks

Edit: it's always been noisy, but I think the auto-bleed used to work and masked it for a year, and ever since the valve broke it's been more noticable.

 

[Nige F]

I
Could I extend the vent and feed back to before the pump under the floorboards - it will be a large horizontal run.

.

IF you can get a slight rise on both - back to the F+F tank , you`ll probably get away with it .And make provision for a drain cock - so that you can backfill through it with someone watching the F+E tank How long is the large run

 

[eurodave]

The run is about 15ft but then would go back vertical for a foot to connect to the pump inlet pipe.

I'd rather do it right. I think I can probably sort it through the loft with the same route as the hot water tank header pipe.

Anyone know what the pressure looks like on this and when it's negative? Probably depends on if the HW demand is on. I am guessing when 'HW only' is on that it's a closed circuit and potentially dangerous because there's no vent. Would a boiler also have a safety pressure valve?