I have a ‘back boiler’ within my chimney breast. I had to turn the water mains off the other day (which I have done before with no problems) as soon as I reconnected the water after doing no work the cold water is flowing fine but the hot water is fine for a few seconds but then dribbles.
You had to turn off your cold water supply for what purpose? Did you break open a pipeline or joint and allow air into the system? Perhaps you would be so kind as to explain what exactly you did and why to get this result. Simply turning a valve on or off would not normally create any problem unless the jumper valve or seat in the valve stuck or jammed.
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