Isolating the hot water to change a tap washer

I need to isolate the hot water to a sink to replace the tap washer but under the sink there is no means of isolation.

How do i go about this? The hot water is supplied from a boilermate 2000.

Is there a means of isolation valve on the boilermate?

Thanks in advance.

Just turn off your stopcock inside the house or outside.
Turn the tap on, when the water stops change the washer.
Mike
MGC/H2O
Norwich

Thanks for the Reply Mike,

a couple of further questions.

Is the hot water fed by the water main pressure, and how much water should come out of the tap, Is it until the pressure /gravity drops or will the cylinder empty before the water stops.

Also is there any possible problems when the water pressure is applied again?

Thanks again

Please read your user book or manuals on your units.
And read my post to you again.
Enough said really.
And have you looked under the sink to see if an isolation valve has been fitted to the pipe work supply the tap?