Is this an isolation valve?

Alan · 2010-10-06T09:14:06+00:00

I'm getting a small leak (the occasional drip) from the tap on an isolation valve which is part of the top-up for the CH system. The top-up is a simple flexible connection with an obvious isolation valve with handle on one side and something which looks like an isolation valve but has a hex nut where I would expect a slotted screwdriver fitting or a handle.A quick check shows that the hex nut will go through more than a quarter turn and is currently turned as far clockwise as it will go. I'm wary of turning it too far anti-clockwise just in case it's going to come unscrewed, fall out and coverthe floor in waterHere's a photo of the set up offending item is on the left - here's a close up photo've had a quick look through various web-sites but I've not come across an isolating valve looking like this.Can someone enlighten me please - if I turn the nut fully anti-clockwise will it shut off the system or will it just fall out?Alan