My protherm 100EC GC No 47-920-33 combi boiler is showing FO- with no hot water for us. My plumber who 'fixed' it yesterday -and the handbook -say this is due to low water pressure. It has gone again this morning and I have found water dripping from an aperture at the bottom of the boiler. What is happening? Can I safely plug the leak with bluetack or something til the plumber gets back on Monday?