Hot water coming from cold water taps

[russtobin]

Have got hot water coming from upstairs cold water taps. Nothing has been recently changed or adjusted.
System boiler connected to Heatrae Sadia CL210 unvented cylinder.
Anyone got any ideas as to what could be causing this?

 

[king of pipes]

It's probably a faulty non return valve in a shower or mixer tap you can prove this if you can isolate said shower or tap . Kop