The pressure seems fine on the boiler, but water comes out of the pressure release pipe. I have no idea when this happens, but it does not happen continually. How can I stop this from happening? I drained the tank, but this did not help.

The pressure relief valve releases water when

The system has to much water pressure in it. This is usually caused by the auto fill valve going bad or someone opened the manual fill valve allowing too much pressure to build.

If the pressure relief valve is defective it will trip and spill water.

If the units control becomes shorted or frozen in the on position the boiler will keep firing and creating hot water when there is no call for heat. This will trip the pressure relief valve also. This last item can be a dangerous situation and in all cases I recommend you call for on site service.