An automatic cold water supply valve for a boiler is provided to reduce unnecessary electricity or gas consumption for operating a heater because the cold water is automatically provided to the heater when the temperature of mat falls lower than the temperature which user sets up. An automatic cold water supply valve(V) for a boiler comprises a cold water inlet port(12), a cold water outlet port(14), a cold water supply pipe(10), a magnetic field coil unit(20). The cold water inlet port intakes the cold water. The cold water outlet port blocks the cold water with a packing(16) screwed up in the inside thereof. A pair of guide grooves(18) are formed from the cold water inlet port inside to the packing screwed inside the cold water outlet port in the cold-water supply pipe. A coil(C) in which the magnetic field is formed is rolled on the magnetic field coil unit when the power source is supplied to the outer circumference of the cold-water supply pipe. A cover(22) protecting the coil is integrated with the cold water supply pipe.
