Water hammer on hot pipes when cold outlet is open.

[GiZmorob]

Hi all. This is a new one on me but got wate hammer on hot water pipes when any cold water outlet is open. This could be a toilet flushed or tap open to full. Also it is quiet if you open a second outlet. This is confusing me completely. No plumbing work has been done but gas work has so the boiler was turned off at mains. Can't think why that would cause this. Anyone got any idea? Thank you.

 

[hammers4spanner]

deadleg

 

[kris]

Your cause will be either a mixer shower cartridge or a tap or stop valve . You need to look at those to eliminate possible causes.