Need to replace tap washer - no isolation valve

[St23]

I need to replace the washer on my hot water tap in the utility room.

The pipe does not have an isolation valve fitted.

My hot water supply comes from copper cylinder which is in the airing cupboard in my bathroom. Cylinder is fed by plastic cold water tank in the loft.

Do I need to drain the copper cylinder? How will I stop water from loft tank feeding it?

Is it safe to drain either the copper cylinder or the loft one?

Is there an easier way than draining?

[stoneyboy]

St23,
There should be a valve either near the cold tank in the loft or in the airing cupboard in the pipe which goes to the bottom of the hot water cylinder.
If neither of these exist turn off your mains water, drain down the tank in the loft by turning on a cold tap in the bathroom (preferably the bath), once the cold tap has stopped running turn on a hot tap (preferably the bath), and this should very quickly stop running. Now turn on the tap in the utility room and this should also stop running fairly quickly.
You can now work on the utility tap - there is no need to drain down the hot water cylinder.
end