What keeps making these leak. Replaced 2 already they start leaking in less than a month

Just tap the pressure release with screwdriver or something easy.....will drip if you dont and usually fixes the problem...

If you have replaced a temperature and pressure relief valve and it continues to drip, you may need a thermal expansion tank to absorb excess water pressure in the plumbing system. A thermal expansion tank is needed when the water heater is installed in a "closed system", which prevents water from flowing back to the source. Many homes with water meters and/or pressure reducing valves have closed water systems. On well water systems, a closed system may exist if there is a check valve between the water heater and the well pump-tank. Thanks - Gabe