One isolating valve on both loft tanks inputs?

Question

Just after the mains stopcock under my kitchen sink there is a tee, one pipe to drinkable water+washing machine and the other to the loft cisterns. ( This is 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?

Answer 1

There may be (or have been in the past) rules or conventions about the F&E tank especially on solid fuel systems, to ensure they can't accidentally run dry.

However in the past some F&E tanks for gas central heating were installed without any cold supply at all, were initially topped up with a jug, and then left to get on with it. It was assumed there would be negligible evaporation loss, and the advantage of a very limited quantity of water to escape in the event of a leak. This was often on housing scheme work where hundreds of houses were done in one job and the saving of hundreds of ballvalves would mount up.

I believe current regulations require a service valve for every outlet.

It may also be useful to fit a drain tap at the base of that riser to the loft, so that pipe can be drained down if necessary.