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Help Needed With Expansion Tank Valve Setting

Postby NormanW » Tue Dec 12, 2017 7:43 am

This is the tale of a southern European plumber, and me trying to fix the faults he has left me with!

I had a local plumber install central heating. It is an open system, heated by a 16kW wood stove boiler. In the unheated, uninsulated bare roof tile loft, typical of here, he installed a small 10 liter expansion tank.
hot expansion.JPG
10 Lt expansion tank in situ

Unfortunately he did not insulate either the tank or the pipes and last winter during some extreme cold, I had a number of bursts, including one on a 22mm elbow from the cold outlet of the tank. (sorry, can't get the picture to rotate to portrait)
cold burst.JPG
split elbow joint

I am now fixing it as he has refused, unless I pay him again, but what I have found leads me to question the settings and would ask for forum members help please.

There are three pipes, a 15mm overflow pipe, a 22mm feed to the top of the tank which is from a Tee piece on the hot side of the system, and a 22mm cold outlet from the bottom of the tank, also from a Tee piece on the cold side of the system.
cold valve .JPG
Valve and pipework

There is a lever ball valve close to where the cold pipe exits the loft to the outside - all the pipework runs outside the building and has now been properly insulated. When I went to replace the 90 degree elbow, I found the valve was set in the closed position. It is not visible for the loft hatch.

Question: What position should the vale be set to? Open, or closed?

My understanding of an open system is that as water heats, it expands. This expansion is taken up by water flowing into the expansion tank. But I thought that then, as the system water cools and contracts, the valve should be open so that the expansion tank in essence becomes a header tank and refills the system?

In running the system last year I found that the overflow was often running and I was also having to top the system up every week as well. I wonder if this is the reason.

Thanks for reading - any advice would be appreciated.

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Simply Build It

Postby NormanW » Tue Jan 02, 2018 6:45 pm


I think I found the reason why the ball valve was off - when I repaired the various pipe fractures and opened the valve, the valve leaked. Close the valve and the leak stops!!??! So I presume my lazy plumber found it easier to turn it off than replace it...

I can see no reason to have a valve on the cold return side when there are no others and no drawing I can find online show a valve anywhere except on the sump drain.

I cut the valve out, replacing it with 22mm copper, all now insulated and immediately found that the long bathroom towel rail, which would never bleed properly or heat now works.

I think I have answered my own question
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