I have been getting an 04 error on my linea 24 boiler. Pressure gauge 1bar. Tried resetting at mains, tried emptying and refilling system, all no good. Previously i had got it working by dabbing the pressure release valve for a second. I could hear air gurgling then it would burst back to life. Now all i get is water coming out the valve and no response. Any help please as its getting cold. Thanks