Originally Posted by transmitterdan
Glad you survived Gonzalo and I hope all will be back to normal soon.
A non-return valve isn't mandatory. The hot water
will back up into the cold pipe a little but if there are no cold taps close by it isn't a problem. When hot water
is drawn from a tap then cold water flows into the heater. There is no tendency for hot water to flow backwards then.
If there is no non-return valve, and the cold water tap is opened, it will considerately draw back the hot water. But length or runs factors in. Had this same problem with Blue.
Gonzalo was nasty, eye over us for 2 hrs. Back side wind
from the NW was strongest and did more damage than SE quadrant. Blue needs new paint