If I close off the cold feed in the loft (feeds hot tank floor below and bathroom) it dribbles and eventually lukewarm water comes out. If I let that run long enough there is an air lock in the hot feed when I restore the cold. Am I right in thinking that the dribble is water coming up from the bottom of the hot tank being vacuum sucked out up its cold feed pipe (the cold feed divides in the loft just below the base of the cold tank there)? There will be no cold head as the cold tank is shut off (gate valve on output)? Thanks.
PS the airlock wiill clear on its own if I leave the hot tap on for a while.
PS the airlock wiill clear on its own if I leave the hot tap on for a while.