Small plumbing snag: occasionally there's a bit of hot water coming out
of my cold water taps: I open a tap, the water runs cold for a few
seconds, then suddenly hot for another few seconds, and then cold again.
And if I turn off the water at the mains and open a cold water tap, the
water from my hot water tank eventually drains out through the cold
water tap. Shouldn't there be some kind of non-return valve ensuring
that the hot water doesn't drain back into the cold water side???