Open Vent certral heating system with no vent pipe

Sandy43 · 12 May 2009

I have Open vent central heating system with mid-position valve for heating and hot water.
The cold feed comes from the expansion tank in a 22 mm pipe but there is no VENT pipe for any expansion of water.

I wonder whether I do have to have this pipe?
I asked the plumber who installed our boiler the question. He said that
as we have 22 mm cold feed pipe then we do not need it, but recently
I looked into the service manual and this shows a diagram that indicate that I should have it.

I am bit confused whether I should have this pipe or not?
I would appreciate a prompt reply on this issue.

doitall · 12 May 2009

Lets just say the vent is a safety valve for when things go wrong like the cold feed/expansion becoming blocked.

gas4you · 12 May 2009

You have a combined feed and vent. This was used/introduced by BG many years ago to get round pump over problems if I recall properly.

namsag · 12 May 2009

It is actually specified by some manufacturers of low water content boilers. Which you may have had in the past.
But if new boiler instructions ask for seperate cold feed open vent then get him back, Which boiler do you have.

doitall · 12 May 2009

gas4you said:
You have a combined feed and vent. This was used/introduced by BG many years ago to get round pump over problems if I recall properly.

He hasn't got a vent Dave combined or otherwise.

I should say to the OP that the vent isn't for expansion, that takes place in the cold feed.

namsag · 12 May 2009

DIA.....Air will vent up and out of the cold feed pipe, Hence it being called combined and as you know occasionally they have a tee just as cold feed comes out the tank with a vent pipe over the top

doitall · 12 May 2009

namsag said:
DIA.....Air will vent up and out of the cold feed pipe, Hence it being called combined and as you know occasionally they have a tee just as cold feed comes out the tank with a vent pipe over the top

So are you saying you don't particularly need the vent pipe over the top.

Kev F · 12 May 2009

not as far as im aware

namsag · 12 May 2009

Yes thats what i am saying as per manufacturers instructions , eg servowarm , thorn apollos amongst others

doitall · 12 May 2009

New one for me

namsag · 12 May 2009

Very common DIA surprises me you have never seen it , have a look at www.partsarena.com/baxi bring up the myson economist 30b/40b or thorn apollo 15/30si and they have a couple of different ways of doing it

Dave this was not brought in by BG it was manufacturers

doitall · 12 May 2009

Probably because I don't do Domestic

namsag · 12 May 2009

After seeing your picture on labeling pipes i`m glad i dont do what you do,

The theory of the combined cold feed open vent is because the water is always moving (expanding up the cold feed) then in theory it should not block and don`t think i have ever saw one that has

doitall · 12 May 2009

namsag said:
After seeing your picture on labeling pipes i`m glad i dont do what you do,

The theory of the combined cold feed open vent is because the water is always moving (expanding up the cold feed) then in theory it should not block and don`t think i have ever saw one that has

I must dig the top half out and post it.

Sandy43 · 12 May 2009

doitall said:
namsag said:

DIA.....Air will vent up and out of the cold feed pipe, Hence it being called combined and as you know occasionally they have a tee just as cold feed comes out the tank with a vent pipe over the top

Click to expand...

So are you saying you don't particularly need the vent pipe over the top.

22 mm hot water pipe comes from the boiler and is teed up for the cold
feed with 22mm pipe. The there is a Pump and it is further teed up with 15 mm for by-pass which it seems an isolator connected to Return.
The hot water has mid-position valve. One side goes to immersion tank and this has auto air trap bottle. The other side goes to heating and that is
aso teed up with 15 mm and some thing like end cap with a screw in the middle is soldered on. I suppose this is used to bleed air out on heating side. Bottle air trap is used the let the air out from th hot water side.
But definitely there is not vent pipe.

diynot

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Open Vent certral heating system with no vent pipe

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