Mysterious pipe All aspects of plumbing questions and answers, help, tips and information

[ifw]

I am looking to replace my hot water tank with a larger one and possibly replace pipework from cold water tank in loft to hot water tank.
On investigation the expansion pipe from the hot water cylinder appears to tee off by the cold water tank and returns via a cavity wall to the bathroom. My query is what does this extended pipe run do if anything??
House was built in the fifties and pipework appears to be original.
Grateful for any indications.

[andy.blackpool]

You'll probably find that the supply to the bathroom has been run off the vent pipe

[ifw]

Thanks for that, it does appear that way but there is also a hot water supply going direct from the cylinder connection to the bath and basin.