Hi not used this before so please bare with me... I have a worcester Bosch 230 combi - boiler and it keeps losing pressure suddenly. The reset button pops up when this happens. To get it going again I first refill the system by opening the loop and then press the reset button. It loses pressure within 30 to 45 minutes. I have checked for leaks but nothing visable can be seen. Not sure what else I could do...Any suggestions wold be greatly appreciated and potentially life saving in this weather