Yeah I tried it with the water running but it didn't make any difference. It doesn't matter if the switch is up or down, the water runs, so no failsafe. I don't know how they work but it's probably scaled up as it's before the water softener.
The story here is that I had a T leave the water on at the stop tap when they went away in winter in about 2010, and the result was a leak which caused T to be out of the property fro about 8 weeks, 2 weeks of my time coordinating the repairs, and an 8k insurance claim.
Fitting the Surestop is just a way to make sure it is easy for the T to switch off the water, and easy enough that I can put something in the rental agreement for nights away that can be enforcible later.
As you say @PeterStarck - that requires it to be reliable.
The oldest one I have in nearly 5 years old, but that T is still there so I can't take it out to examine.
My current arrangements for new rentals tend to be:
1 - Magnaclean on heating circuit when new rads or a new boiler are installed.
2 - LIFF Limefighter 2 (magnetic not electrolytic which is the Limebeater) and Surestop fitted with switch above worktop or inside cupboard.
3 - Term in the rental agreement that the Surestop be used when away overnight. I encourage them to use it when out for a day, and tell them the story of the Great Leak. I think that requiring Ts to croink around with a stop tap every time they are away overnight would make such a clause unenforcible due to being unreasonable.
I know that people have opinions about water softeners. My experience at home in the same geographical area is that a Limefghter 2 made a significant difference when we fitted one. And since they only cost £20-£30 compared to £800-1000 for a boiler it seems a no-brainer.
I will need to check which order the things are in in the system. Logically the Surestop has to be on the mains side if it is to be a stop tap replacement. Perhaps some thought needed there and to accept that it is a secondary stop tap (and perhaps go for the remote switch but non-WRAS version which would save a few £££).
Ferdinand