Do you have a check valve (backflow prevention or other that allows flow 
one direction only like a diode)? If so, cold water comes into the 
system and thermally expands. This added volume has to go somewhere. If 
not released can build pressure maybe as high as over 100 psi. and force 
open valves, force joints apart, or even burst pipes. If there is a 
check valve, there needs to be an expansion chamber. Best have a rubber 
bladder to ensure the air is always there. See:
http://www.buygasappliances.com/ViewProduct.aspx?categoryid=34&productid=90

Our water meter has a check valve built in, and then we are required to 
have a double check valve reduced pressure backflow preventer since we 
have a cistern where we  collect roof water which is used for everything 
except th kitchen cold water which is potable.

Sean Breheny wrote:
> Hi all,
>
> Happy Easter!
>
> I struggled a bit with whether to make this OT or EE (Everything
> Engineering), but here it goes:
>
> One of the toilets in my mom's house is leaking. The problem is that
> the fill valve never closes completely. The interesting thing is that
> this is about the fifth time that this has happened in 15 years or so.
> Is it normal to have to replace that valve assembly every three years?
> All the sites I've checked indicate that the flapper is most often the
> cause of leaks, but with this toilet, it has never been the cause of
> the leaks. She never uses in-tank cleaners or anything which should
> hasten the demise of the valve. The only thing I can think of is maybe
> high or erratic water pressure? Her water is not very hard. It may be
> chlorinated but I don't taste it as excessive.
>
> Any ideas?
>
> Thanks,
>
> Sean
>   
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