how do I isolate the hot water system if it doesn't have a gate valve ?

There should be a gate valve near to your hot water tank. Close this valve clockwise. then turn on the highest hot tap, then the lowest hot tap, this will drain the water out of the pipes. When the water stops running you can then remove the tap. I suggest that you install service valves to all of your taps to make life easier in the future. Cheapest place for these is Screwfix Direct. Hope this helps. Don't forget to bleed the pipes of air.

Brian
February 2009

drain it down

xxx
February 2009