On one rad at home, which was working last year but is now not, there is hot water getting into one end, which has something similar to this pic in place - the usual valve but with the bullet like piece on it. The water is not going past this. The other end of the rad has a TRV on, which even when turned up to full makes little difference although the other day the rad did begin to get slightly warm. However, I wonder if this thing is creating a problem - it has a square pin which can be released (as if it were a bleed valve), but I'm reluctant to do anything until I know more.

It seems to be the only rad that has this addition. Confused...

Screwfix.com (http://www.screwfix.com/app/sfd/cat/lrgimg_popup.jsp;jsessionid=Z3YMBAJEQTJPKCSTHZOSFF Q?productId=83588&imageNo=null&ts=83950)

While we're at it, what is the rationale for only bleeding rads when the heating is off - surely the water is under pressure when the heating is on thus it is easier to expel air. Or is it just a safety thing?

Thanks

Andy

I am only a DIY person not a plumber. The bullet bit is to allow you to drain the system. So presumably it can be opened and closed to let the water out.

That allows you to turn off the rad and drain it without draining the system.

Mog

It allows you to drain only the rad, but beware that you have undo the screw then put the hose on especially if your system water is black, if spilt it will stain.
i would go with these instead.
Lockshield/Wheelhead with Drain Off - available at Plumbworld (http://www.plumbworld.co.uk/354-2784)

as wrxcraig has said it can be used to drain that one rad or it can be used to drain the whole system

I'd check first that the lockshield valve isn't shut, (open it about a half turn for a bedroom and a full turn for the lounge), then remove the thermostatic head from the TRV, undo the nut around where the pin protrudes, and free off the square headed pin inside. Have a cloth around the base of the TRV while working to soak up any water that weeps out, it doesn't spurt, don't worry.

Alcazar

It's a drain, cock.