The Temperature Pressure Relief Valve on my 9 year old AO Smith water heater has started to drip. It only does this when we use our central air. Any ideas on why or what I should do about it? I am planning on replacing the valve tomorrow, but find it curious that it only leaks when the air is in. The water heater is about 4 feet from the furnace, which is what circulates the air. It's a forced hot air system. Any help will be appreciated.