Expansion Vessel position

[Hoof Hearted]

I have a 3 story - 5 bedroom house which i've been renovating for a number of years. When I had the central heating installed, most of the house wasn't ready. So I got the plumber to install the boiler and 6 radiators, with the intention that I would add other radiators later. Eventually I think there will be 16 radiators. Currently i've got 9.

The plumber told me at the outset that I would need an additional expansion vessel. I've bought this and hope to be fitting it soon. All the documentation i've seen suggests that I should be fitting it close to the boiler on the return pipe. This creates a problem because the boiler is above the back door in the kitchen and all the pipes go upwards into the ceiling above. Because of the location of the boiler nothing can be mounted underneath, and the vessel is too large to mount above the boiler. However there are 2 other places i've considered.

1. I could fit it under the lounge floorboards. This would be on the lowest part of the circuit, but it would be 17 metres from the boiler and intrude downwards into the cellar. So i'm not keen on this.

2. I could fit it on the top floor. There will be 4 radiators up there and the pipework will pass through a cupboard. This would be 7 metres from the boiler and on the highest part of the circuit. This would be my ideal place to mount it if it doesnt cause problems.

Comments please? and I would like to know which way up I should mount it.

 

[erj]

mount it so the air valve is at the top, if you can not fitt it next to the boiler, go for up stairs.
Why not get a pro to fit it?

 

[Best]

Surely the heating guy should have sorted it out at the time, knowing it was needed later? Also, the size of vessel & what air charge needed in it should be an engineers job.
Ideally should be close to the boiler, on the return pipe on the suction side of pump, but fitting the second e/v upstairs will give the system the extra expansion. You need the vessel accessible for represssurising or replacement.
Water side to top, air charge side to bottom, IMO, but will work other way. Make sure the air valve is easy to connect a pressure gauge or air pump to.

 

[Hoof Hearted]

I'm glad it can go upstairs. It will go in a cupboard where it is easily accessible. But I can see I got 2 different answers regarding which way up it should go. Is it air valve to the top? Or air valve to the bottom? I've now found the supplied leaflet which shows the air valve at the top. So I assume this is correct?

I would have thought if the valve is at the top, it will always have an air lock in it because there is no route for the air to escape, but perhaps this doesn't matter?

I take your point about having a professional fit it. The original plumber didn't install it because it was not practical to put pipework in that part of the house at the time. He told me that I needed the expansion vessel, but never mentioned that it would need charging. I assumed that it would be ready to go when I bought it.

 

[mike-c]

You could always split the difference and fit it sideways :mickey:

 

[Best]

The vessels are precharged but you must have the air charge to suit what the water pressure charge will be. Usually the air charge will be just less than water charge when system is cold.
The air does not vent from the vessel. It is trapped in one side of the vessel which is divide off by a flexible diaphragm. The air is only lost through natural ways, just like a car tyre & needs pressure checked every year & topped up if necessary.
Vessels are fitted air up or down, but I think the water side is better to have the ability to vent to another pipe if possible. Will work fine either way.

 

[Hoof Hearted]

The air does not vent from the vessel. It is trapped in one side of the vessel which is divide off by a flexible diaphragm. The air is only lost through natural ways, just like a car tyre & needs pressure checked every year & topped up if necessary.

hmmm.... Are you talking about the air valve side? Yes I know there is pressurised air in the air valve side. I would have expected the other side to contain water from the central heating system. But if the vessel is mounted with the air valve pointing upwards, then there will be an air lock under the diaphragm which cannot bleed away anywhere. So there will be air on both sides of the diapragm. Perhaps this is normal?

 

[Best]

hmmm.... Are you talking about the air valve side? Yes I know there is pressurised air in the air valve side. I would have expected the other side to contain water from the central heating system. But if the vessel is mounted with the air valve pointing upwards, then there will be an air lock under the diaphragm which cannot bleed away anywhere. So there will be air on both sides of the diapragm. Perhaps this is normal?

That is kinda my logic (although the air is said to absorb into system). This is why I always understood it is good practice to fit the water side up. Nice if it joins to a pipe to the side or above it for this reason. They seem to last okay whatever way fitted. They are in gas & oil boilers every direction. Just be careful not to be tempted to overcharge the system when refilling as this can cause vessel to corrode later & do add inhibitor.

 

[Hoof Hearted]

I will mount it valve side downwards then. In terms of inhibitor, I use Fernox Alphi 11 antifreeze because some of the pipework in the cellar goes through an external wall where it cannot be lagged. I assume this type of inhibitor will be ok.

 

[mfgs]

Ideally the expasion vessel would be close to the boiler on the return, but as in your case , it isnt always practical. It can go anywhere really and it will still do a job. You wont get an airlock on the water side of the diaphragm and it wouldnt matter even if you did as when the pressure in the system increases it will still push against the rubber diaphragm anyway whether its water or air there.

 

[stevetheplumber]

no one has mentioned there shouldnt be a valve of any sort between boiler and vessel

 

[Hoof Hearted]

no one has mentioned there shouldnt be a valve of any sort between boiler and vessel

Thanks Steve. This reminds me that i've got an interesting problem now... When the plumber did the first phase of pipework for me, he left me with 2 x 22mm pipes sticking up into the loft with gate valves on them. I dont know which of these is the return back to the boiler. I wonder if one of them will be louder than the other if I listen with a piece of wood against my ear.