Ive got a 500L Xline tank and recently it's stopped filling up properly. Mains water pressure is about 80psi so that's not the problem. I've contacted Xline as this is second time it's happened and they are sending out a new RO unit, I've changed the carbon / paper / resin in Oct last year, mains is 320ppm so should I be changing filters more often? Reading have just gone up to 002. System flushes correctly for first 5 mins then just shuts off? Any ideas would be much appreciated.