Hey Guys! I'm newly registered to the forum but have been an avid reader of all advice regarding my central heating boiler. It is a Vaillant Ecotec Pro 28 and was fitted about 3 years ago, it has been great until last year (around this time of winter) when the outside condensation pipe froze up, it backed up and started dripping water from the trap, it could not be defrosted with boliling water so I severed the 32mm outside and removed the rod of ice that had built up. Unfortunately it is fitted on the most exposed wall of the downstairs kitchen where the wind blows the hardest. Anyway, to cut a long story short it recently started to show the common F75 fault, I checked and repressurized the EV to 0.9bar, bled all of the CH heating system twice, checking for dead legs but the whole thing is fine and red hot when working. The trouble is when the system gets to up to temperature or there is demand for hot water when the boiler tries to restart the CH system, it goes through the S1-S4 startup and then F75's, the only way I can get the system to fire is to add a little more water via the fixed filling loop and restart the boiler, the display also shows a S91 code (pressure over 2.9 bar) which is not suprising as the visual gauge is always in the red for the boiler to work. Water is constantly coming from the blow off pipe outside due to the excess pressure. I have a new pressure sensor switch on its way which I should hopefully receive tomorrow all being well, I will fit this as soon as I get it as a matter or course. So I'm my summing up before any of you kind gents can advise me, I believe the pressure sensor switch is knackered telling the system I need more water pressure, when the system expands when working at temperature the excess water is being driven out via the blow off pipe. the system water then cools pressure drops causing the F75, The frozen condensor pipe I believe is a seperate issue due to the weather!? I took the condensor bottle out yesterday to find it was full of some kind of metal sediment, I cleaned and refilled this to 10mm from the top as per the manual. I need to keep this boiler running as I have a severely disabled 9 year old daughter who needs to be kept warm. All and any advice appreciated, thanks in advance Kind regards Steve.