CH under-floor drain valve problems

[nemo2000]

Years ago when my kitchen was refurbished the CH pipework was fitted under the floor with a 'branch pipe' which went out through the wall and discharged into the outside gully. This was fitted with an ordinary isolater valve, so that the system could be drained as necessary without having to mess about with attaching hoses to a conventional drain-off and then having to have the outside door open while the system drained out. The isolator valve was operated by putting a long screwdriver through a (covered) small hole in the floor and engaging with the slot in the valve spindle. Very tidy and handy...until now....

I tried to open the valve today to drain the system in order to fit a TRV to one of the older radiators elsewhere in the house. The valve barely moved, just enough to let a dribble out. Problem is, it won't shut now :-( So now the outlet is dribbling away down the drain and the ball-valve F&E is open just a little and feeding the tank continuously to compensate !

So now probably, once the system is drained, I'll fit a conventional drain-off to the radiator in the kitchen - no problem with that. But short of ripping up a lot of flooring (vinyl floor covering + hardboard sheets + T&G floorboards) to get at the old valve, how can I stop the dripping? If I just cap off the end of the outlet pipe, I fear the valve spindle will leak - it's showing signs of having done that in the past. Is there anything for example that I could inject up the branch pipe that would 'block up' the valve?

Help !

 

[nemo2000]

Fortunately, I found after further careful investigation that it was possible - because of the location of the valve - to pull back just a small corner of the vinyl flooring and remove the 'trap' which had been left in the floor when the valve was fitted. With better access to the valve it was possible eventually to lever it open and rain the system after which I replaced it with a more robust version. Hopefully now it will be trouble-free for many years....?