Hm. That's starting to feel like a red herring, but where does the outlet go, have you checked it, and is it blocked?rgbd said:Will try your idea about opening the gate valves tomorrow but I can't open all 3 because 1 of them drains the whole CH system down and empties the F&E. I think the 1 for the HW only drains the pipework leading to the taps and doesn't drain the HW cyl. Don't know what the CW one does as I have never opened it but I would imagine it does the same as the HW one.
Manual. In theory it doesn't matter because the MZV merely controls the flow from the boiler when the pump is on, and with the pump off and the MZV shut water can still make its way up the feed to the F&E, but in case you have an air lock somewhere it's simplest to set the MZV open manually when doing this investigation.rgbd said:Should I set the Zone valve to AUTO or MANUAL while observing the F&E or try both to see if there is any difference ?? I assume that I will have to turn the mains off at the same time ??
BTW, when you shut off the mains (previously), and opened a cold tap, did you get a constant and fast drip of water? For example, 1cm per hour for a 4 gallon F&E cistern would equate almost exactly to around 1 litre of water, so the tap would almost be running...