I often find that the rubber seal on drain off cocks stick inside and the valve just unscrews and little or no water flow. Sometimes there are other ways to drain the system but if not how do you get the rubber washer out without getting water everywhere. I have one stuck on the primary circuit of a gravity fed cylinder from a wood burner, I could bung the vent and cold feed but unfortunately it is an old property and the loft access is tiny and the only way to get to the F&E tank is through a neighbouring property. The customer has indicated that this may not be possible. Any tips would be appreciated.