Open vent system.

[Lee Appleton]

Hi, just wondering if anyone could provide me with advice please on an issue I am having with my open vent system.
I have recently installed 3 new rads and lost some circulation, when I went to the the loft a noticed that the cold feed was very hot, I have been told previously that header tank was too low and close to the pump as I have also have rads on the same level in the loft conversion. I decided to fit a new header tank in higher position and further away from the pump, but I left the open vent over the old tank, I seemed to had fixed the over heating of the CW feed pipe but when the pump stops I get cold water from the open vent pipe, I also have air in and around the filter. Any assistance would be appreciated.

 

[John.g]

Hi Lee,

I too have a open vented system for the past 49 years which never pumps over or gets air in the system simply because it can't as it was installed with a combined vent and cold feed (see below).

You might post a photo of where your cold feed joins the system, the preferred way with a lot of open vented systems is to have the pump on the flow side of the boiler, so you will/should then have, from the boiler, vent, cold feed and then the pump with the vent and cold feed no more than 150MM apart and pump also close by if possible. This, theoretically should work equally well but I have my doubts.
If you are getting cold water from the open vent pipe when the pump stops then it will pull air in after the water stops flowing and you will be constantly venting air from the system. Have you two header tanks now or what since your venting into one and providing the cold feed from the other.

You might also post details of pump and its present settings.....did you always have this problem or has it only started with the installation of the new rads?.
Was the pump renewed recently?.

 

[Chuck]

but I left the open vent over the old tank

If I've understood you correctly, this probably your problem. (Or at least one of them.)

Can you provide a diagram showing the relative heights of the key parts, please?

 

[Lee Appleton]

Hi Lee,

I too have a open vented system for the past 49 years which never pumps over or gets air in the system simply because it can't as it was installed with a combined vent and cold feed (see below).

You might post a photo of where your cold feed joins the system, the preferred way with a lot of open vented systems is to have the pump on the flow side of the boiler, so you will/should then have, from the boiler, vent, cold feed and then the pump with the vent and cold feed no more than 150MM apart and pump also close by if possible. This, theoretically should work equally well but I have my doubts.
If you are getting cold water from the open vent pipe when the pump stops then it will pull air in after the water stops flowing and you will be constantly venting air from the system. Have you two header tanks now or what since your venting into one and providing the cold feed from the other.

You might also post details of pump and its present settings.....did you always have this problem or has it only started with the installation of the new rads?.
Was the pump renewed recently?.

Thanks, I forgot to mention I also extended the open vent up in to the apex of the roof so that it was about 15" higher than the header tank water level. But its positioned over the old header tank which is on the other side of the loft about 6' apart. I will attach photos of the system when I return from work. Thanks again. Lee

 

[Lee Appleton]

If I've understood you correctly, this probably your problem. (Or at least one of them.)

Can you provide a diagram showing the relative heights of the key parts, please?

I will pop a diagram on once I return from work, thank you

 

[Lee Appleton]

Hi Lee,

I too have a open vented system for the past 49 years which never pumps over or gets air in the system simply because it can't as it was installed with a combined vent and cold feed (see below).

You might post a photo of where your cold feed joins the system, the preferred way with a lot of open vented systems is to have the pump on the flow side of the boiler, so you will/should then have, from the boiler, vent, cold feed and then the pump with the vent and cold feed no more than 150MM apart and pump also close by if possible. This, theoretically should work equally well but I have my doubts.
If you are getting cold water from the open vent pipe when the pump stops then it will pull air in after the water stops flowing and you will be constantly venting air from the system. Have you two header tanks now or what since your venting into one and providing the cold feed from the other.

You might also post details of pump and its present settings.....did you always have this problem or has it only started with the installation of the new rads?.
Was the pump renewed recently?.

Hi Please find images of the layout attached, as you will see the open vent gose up to the roof apex at an angle and sits above the old header tank, the new header tank is across the loft about 5' away from the open vent, and the waterline is at about 5'5" which is about 2.5" above the outlet. The outlet pipe is on a constant fall but it have noticed that it is still getting warm up to the new header tank. I do have rad on the same level in a converted loft. Many thanks for you help hear.

 

[John.g]

I take it the Vent is on the return to the top left of "H", the rad returns come up into the bottom left of the "H" and the cold feed comes down into the top right of the "H". the bottom right side of the "H" are the returns to the boiler via the Mag filter.??

Is the pump pumping away from the boiler (flow side) and where is the boiler located?.

where is the pump located in relation to the "H"?.

Was the system working OK at some stage?.

 

[Lee Appleton]

I will pop a diagram on once I return from work, thank you

I take it the Vent is on the return to the top left of "H", the rad returns come up into the bottom left of the "H" and the cold feed comes down into the top right of the "H". the bottom right side of the "H" are the returns to the boiler via the Mag filter.??

Is the pump pumping away from the boiler (flow side) and where is the boiler located?.

where is the pump located in relation to the "H"?.

Was the system working OK at some stage?.

Hi, cold feed tip right of the H open vent Left of H, pump is pumping away from boiler, and is positioned below the H tot he right about 2' away, boiler is on the floor below.

 

[John.g]

Is the water flow direction down through the mag filter?.

Is the mag filter clean?

Water will always take path of least resistance and with all the twists and turns of that system then IMO its no wonder it shoots up one or the other when the pump is stopped.
I feel you will have to consider combining the cold feed and vent very close together (like mine) right at the header tank and make the cold feed stub in to the vent the same diameter as the vent.

Did the system work at some stage with the old F&E tank/.

 

[Lee Appleton]

Is the water flow direction down through the mag filter?.

Is the mag filter clean?

Water will always take path of least resistance and with all the twists and turns of that system then IMO its no wonder it shoots up one or the other when the pump is stopped.
I feel you will have to consider combining the cold feed and vent very close together (like mine) right at the header tank and make the cold feed stub in to the vent the same diameter as the vent.

Did the system work at some stage with the old F&E tank/.

Yes this system has been ok for some time, its always been problematic due to the height of the old tank and position of the rads on a simular level. All the bend in the open vent have always been there ibhhave just extended the vent upwards so it's above the header tank, as for the cw feed I moved this because of the close proximity to the pump and advice from gas fitters who said that it was too close.

 

[Lee Appleton]

Is the water flow direction down through the mag filter?.

Is the mag filter clean?

Water will always take path of least resistance and with all the twists and turns of that system then IMO its no wonder it shoots up one or the other when the pump is stopped.
I feel you will have to consider combining the cold feed and vent very close together (like mine) right at the header tank and make the cold feed stub in to the vent the same diameter as the vent.

Did the system work at some stage with the old F&E tank/.

Morning, would you suggest that I run the vent pipe near to cold feed pipe and then put a 90 degree elbow on to take it above the the new header tank, also do you think changing the elbows out for bends on the cold feed would help? Thanks for your help John.

 

[John.g]

Don't really know Lee, all I can state with certainty is that mine never pumps over even though I have two rads in the attic with the bottom of the F&E tank ~ 500mm above the attic floor and about 170mm above the rad tops. Oil Fired Boiler and Pump are outside on the ground with the pump pumping into the boiler return.
The mag filter position probably isn't helping either, as its causing a resistance just where its not needed, thought it would be better positioned just before the boiler below, on the return.
Attached are a few more methods of hopefully stopping that pump over, but again can't vouch for them.

What speed setting is the pump on?.

 

[Lee Appleton]

Don't really know Lee, all I can state with certainty is that mine never pumps over even though I have two rads in the attic with the bottom of the F&E tank ~ 500mm above the attic floor and about 170mm above the rad tops. Oil Fired Boiler and Pump are outside on the ground with the pump pumping into the boiler return.
The mag filter position probably isn't helping either, as its causing a resistance just where its not needed, thought it would be better positioned just before the boiler below, on the return.
Attached are a few more methods of hopefully stopping that pump over, but again can't vouch for them.

What speed setting is the pump on?.

Thank you John.

 

[Lee Appleton]

If I've understood you correctly, this probably your problem. (Or at least one of them.)

Can you provide a diagram showing the relative heights of the key parts, please?

Click to expand...

Hi Please find images of the layout attached, as you will see the open vent gose up to the roof apex at an angle and sits above the old header tank, the new header tank is across the loft about 5' away from the open vent, and the waterline is at about 5'5" which is about 2.5" above the outlet. The outlet pipe is on a constant fall but it have noticed that it is still getting warm up to the new header tank. I do have rad on the same level in a converted loft. Many thanks for you help hear.
Would you suggest swappingbtheb90 degree elbow out for bend to improve the water flow, and also move the open vent pipe in line to the cold water feed and then lift above the new header tank? Thanks for you help.

 

[John.g]

Hi Lee, can you just draw that out on a piece of paper "move the open vent pipe in line to the cold water feed and then lift above the new header tank" with rough distances please. Should work if close to the header tank.

 

[Lee Appleton]

Hi Lee, can you just draw that out on a piece of paper "move the open vent pipe in line to the cold water feed and then lift above the new header tank" with rough distances please. Should work if close to the header tank.

Please see attached, I didn't move it as it sits above a old tank but didn't realise it my alter the balance/pressure. Its a very rought drawing. Thank you

 

[John.g]

You might combine the the cold feed and new vent right up at the tank where shown OR maybe consider as a test just combine from the old tank to the existing vent with a bit of piping but this entails blanking off (temporarily) the new cold feed from the the new tank. (or just put a bung in it)

 

[Lee Appleton]

You might combine the the cold feed and new vent right up at the tank where shown OR maybe consider as a test just combine from the old tank to the existing vent with a bit of piping but this entails blanking off (temporarily) the new cold feed from the the new tank. (or just put a bung in it)

To do this I would need a combination valve?

 

[John.g]

No, not at all, just a T like mine.

 

[Lee Appleton]

Hi, cold feed tip right of the H open vent Left of H, pump is pumping away from boiler, and is positioned below the H tot he right about 2' away, boiler is on the floor below.

So I would send water down what is the open vent pipe and cap off the 15mm feed from the right side of the "H" , and just continue the 22mm up above the header tank on a swan neck.

 

[John.g]

That's it, yes.
Ensure both pipes are 22MM.

 

[Lee Appleton]

That's it, yes.
Ensure both pipes are 22MM.

Thank for your help John, as you will have seen from the images my 22mm vent pipe wraps around the back of the hot water tank, would you leave in place and connect the water at a higher level.

 

[Deleted member 123817]

Which tank and which vent are you proposing to use?

 

[Lee Appleton]

Which tank and which vent are you proposing to use?

Just for ease was going to use the new header tank which is about 5' away and about 5'6" off the floor. That way I could swap out the 15mm pipe for a 22mm pipe a and make the connection at the top left of the H,

 

[John.g]

Ideally, the vent should be adjacent to the (new) header tank with a very short cold water stub from the tank (like mine) but should still be ok if I'm interpreting your reply to mean that you will connect the cold water straight across (5ft or so) from, and teed into the vent.
Obviously the connection can't be higher than the tank outlet as no make up water could flow when/if required.

 

[Lee Appleton]

Ideally, the vent should be adjacent to the (new) header tank with a very short cold water stub from the tank (like mine) but should still be ok if I'm interpreting your reply to mean that you will connect the cold water straight across (5ft or so) from, and teed into the vent.
Obviously the connection can't be higher than the tank outlet as no make up water could flow when/if required.

Ideally, the vent should be adjacent to the (new) header tank with a very short cold water stub from the tank (like mine) but should still be ok if I'm interpreting your reply to mean that you will connect the cold water straight across (5ft or so) from, and teed into the vent.
Obviously the connection can't be higher than the tank outlet as no make up water could flow when/if required.

I have attached on of my doggy drawings to show how it would be connected.

 

[John.g]

Drawing as in post 16? where it will be connected to the top right of the "H"?

 

[Lee Appleton]

Drawing as in post 16? where it will be connected to the top right of the "H"?

Sorry as its 22mm I thought it would connect to the top left, it's the cold feed 15mm is on the current top right side or do I need to change this and bung the top left 22mm. I had in my mind connect the CW to the open vent pipe which is top left of the H.

 

[John.g]

I'm getting increasingly confused with this Lee.

Just answer, if you don't mind, these queries one by one.

1. Do you (or have you) propose(d) to run a 22 MM vent to the new header tank?.

2. Do you intend to run a 22MM CW supply to this from the new header tank.

3. Where do you propose to connect in this CW supply to the 22MM vent.

 

[John.g]

Here is a very simple schematic of my proposal, can you just post something similar with yours.

 

[Lee Appleton]

I'm getting increasingly confused with this Lee.

I am very sorry John for the confusion.
1. I did intend to run the 22mm vent pipe to the tank and combine it with cw outlet using the tee as per your system.
2.yes
3.i thought the new 22mm supply would run to the left top side of the H which is the current vent pipe as in the attached. The top right is the curr 15mm cw supply that I thought needed to be capped.
Apologies again I just didn't want to make a mistake.

Just answer, if you don't mind, these queries one by one.

1. Do you (or have you) propose(d) to run a 22 MM vent to the new header tank?.

2. Do you intend to run a 22MM CW supply to this from the new header tank.

3. Where do you propose to connect in this CW supply to the 22MM vent.

Here is a very simple schematic of my proposal, can you just post something similar with yours.

Thank you for your patience John that is exactly what I thought I had to do but didn't explain it very well.

Here is a very simple schematic of my proposal, can you just post something similar with yours.

Thank you for your patience John, thats exactly what I thought I need to do but didn't explain it very well.
I am combining the cw feed as per your drawing using 22mm and capping off the 15mm supply.

Thanks again
Lee

 

[John.g]

Great, go for it!!, how far roughly will the run of CW feed be?.

It would also help if you had/have a isol valve on the cold feed to the (ballcock) header tank and just crack this open to trickle in the water to top up the system sfter partial drain down as it helps the air to escape up the vent and at the same time allow the trickle of water to flow downwards.

 

[Lee Appleton]

Great, go for it!!, how far roughly will the run of CW feed be?.

It would also help if you had/have a isol valve on the cold feed to the (ballcock) header tank and just crack this open to trickle in the water to top up the system sfter partial drain down as it helps the air to escape up the vent and at the same time allow the trickle of water to flow downwards.

From the bottom of the tee of the cw tank to the top of the H left hand side its about 5'. I have an isolated valve so will fill slowly. Thanks again it will be a relief to get it working properly.

 

[Deleted member 123817]

Let's hope so, I was asking the dotted line distance from the tank to where it will Jon the T

 

[Lee Appleton]

Let's hope so, I was asking the dotted line distance from the tank to where it will Jon the T

I will get the tee within an 1" of the tank outlet.