Hi all. Have found this forum immensely useful to learn about the issue of boilers losing pressure. So thank you for all your knowledge so far. I’ll give you the back story, Four year old Vailant Ecotec with a magnaclean filter, serviced annually. All was good until the spring. Was having to top up occasionally as opposed to almost never. Frequency was increasing, then we turned the heating off for the summer and i forgot about it. Fast forward to October and I remembered!! Weekly top ups quickly became daily. Called regular plumber who said PRV and expansion vessel were fine (his diagnosis took 15mins). Said must be a leak under suspended floors as we were losing a litre a day and would clearly notice that if it were upstairs. (I struggle with the litre part as when I top up from say .8 to 1.5 it takes all of 3 seconds with the taps open. Surely a litre wouldn’t pass through that quickly?) For various reasons we haven’t been able to start ripping up the floors (Karndean and tiles ♀️). Last week we did and bought a camera to help the search. So far found nothing (but far from finished as next step is wrecking the engineered wood flooring we discovered under the karndean - heartbreaking!) however this week I haven’t had to top up once. Heating been on as usual but pressure steady at 1.3bar. ive learned a bit and understand about PRV’s etc and it seemed fairly obvs we had a leak. But how can that be?! Very confused now and very grateful for any theories or suggestions from you good people.btw there had been no loss through the prv pipe. Thanks in advance.