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After repacking 5 out of 9 rad valve stems and discovering and replacing the last one of the 1920s vents in the house I came to find I was still losing up to 1/2 gallon of water per week depending on the weather. Checked with the mirror trick and sure enough the Varivalve on the largest rad in the place set about half way and it simply was not closing at all unless it was almost to the fully closed setting. Have since gone with a few more Hoffman 1As and have three days steaming with ZERO discernible water loss. Also will not miss the vacuum breaking noise of the one Varivalve closer to the boiler. Things are looking up!