hot water system expansion tank leaking under pressure

[nick]

Hi,

I wonder if any one can give me some advice.

I have a small diaphragm expansion tank on my hot water system. I have been told to check the water pressure remains above 1 bar when cold, which I do when I remember. I occassionally need to top up the water to achieve this.

At the weekend I noticed it had dropped nearly to zero so topped it up to 1.5 bar. Now what happens when boiler comes on for hot water and heating is water pressure continues to rise. At about 2.8 bar the tank starts to leak around the middle seam. Presumably as it increases the pressure release valve eventually goes and reduces the water pressure.

Does this mean the expansion tank air needs recharging or is the tank itself faulty? (It was only fitted about 2 years ago).

I would appreciate any help from someone who may know what is actually happening. Thanks.

Nick

 

[PlumbBobBob]

if as you say the tank is leaking around the middle seam where it shouldn't be then indeed it is faulty

 

[SimonJohns]

Deffo broken

Need a replacement

 

[nick]

thanks guys.

these tanks dont last long then! Just for info I looked tonight and it is a Watts Industries, 130-CAL-PRO, 8lt capacity tank, max pressure 5 psi. Think I will try another manufacturer!

 

[Best]

Some expansion vessels fail early , on heating systems, due , i think, to the initial fill up. Just a theory though, that I won't try to explain. Do not be tempted to over pressurise system when filling again. If it is replaced with an identical make & type of vessel & assuming system has corrosion inhibitor in it, you will probably have no bother for years - I hope!

 

[armourer]

If the expansion vessel diaphragm fails it increases the pressure within the vessel and on some of the cheaper models it can start to leak at the seams (its only rolled over).

Have the expansion vessel changed and it will be ok.

 

[Best]

If the expansion vessel diaphragm fails it increases the pressure within the vessel and on some of the cheaper models it can start to leak at the seams (its only rolled over)..

Armourer - do you think they are maybe best to replace with welded, seamless type ? I have noticed both types actually rusting but think that is more about trapped water/ oxygen after initial fill, as never happens again.

 

[armourer]

Armourer - do you think they are maybe best to replace with welded, seamless type ? I have noticed both types actually rusting but think that is more about trapped water/ oxygen after initial fill, as never happens again.

Personally I think its worth paying a little more, as if the diaphragm was stronger in the first place, the vessel would not over pressure and a rolled seam would be fine.

 

[Best]

I also think if the pre-charge was set at correct pressure for system before vessel is installed would do no harm. Think most just fit it & that's it. Defeats the purpose of the exp vessel if the pre-charge way too high or low as diaphragm won't flex.