Hi, just after the mains stopcock under my kitchen sink I have a tee, one pipe to drinkable water+washing machine and the other to the loft cisterns (talking about an open vented pumped S-plan system, standard here in UK). I was wondering whether it is safe to add an isolating valve on the latter pipe, placing it right after the aforementioned tee (i.e., under the kitchen sink). I am asking because I've read somewhere that the feed and expansion tank shouldn't have a valve on its input, but I couldn't find a consensus on that, online. I am also suspicious because currently I have an isolating valve just before the bigger loft tank in the loft, not serving the FE tank. Which could be a hint that FE shouldn't have an input valve?