I keep putting the boiler water pressure up and it keep going down and i can`t see any leak, what can be w?

You can't see the boiler losing water, because it is going out of the overflow pipe which is connected to the Pressure Relief Valve. You need to replace this component, as the valve spring has weakened and can no longer hold the water pressure on the boiler. It is a sealed unit and cannot be repaired.Loss of the water will stop your boiler from firing up.