Hi! I have this F75 problem, so far replaced pressure valve and have in my Mitt a Water Pressure Sensor. Ha! Ha! I hear you all, Yes I tried removing it carefully and got a face full of Water plus inhibitor. Please can anyone help? The water pressure was up and down like a YoYo, Im not so sure it is the Sensor but as I have a genuine replacement might as well fit it without getting a soaking What do I do other than turn all the water off.Sorted I have read the manual 3 times and there is nothing to show the removal or installation of the sensor. I am not an idiot as someone seems to think? I as that person to pick up or read the online version of the Vaillant Manual and then apologise. I logically thought out this situation, removed the option of a soaking by draining the system completely and installing the little blighter plus inhibitor. Good luck all of you who use this site As my 1st request was treated with contempt. You know who you are!