Some manufacturers suggest testing the valve every six months or so by raising and lowering the test lever on the valve. This should produce a sudden burst of hot water from the drain line connected to the valve.
More frequent testing can reduce the chance of a leak caused by mineral and corrosion buildup.
However, if a leak results immediately after a test, simply operate the test lever several times to free lodged debris that might be preventing the valve from seating properly. There are a few reasons why your valve is running all the time - wasting water and energy. The valve might be built up with corrosion. Try flipping the test lever up and down a couple of times and tap the stem using a hammer to seat the valve. It should be set on medium for the safest and most efficient operation.