Part drain, complete drain or isolate single rad to fix weeping valve extension?

[LogicalLarry]

Hello Plumbers

I’ve replaced a 540mm high cast iron rad with 740mm high, like for like but still a 20mm valve extension was required.

All was ok until I've spotted a v small leak (like 1 drip per hour) between the valve nut and extension piece.

So I suspect I just need more PTFE + compound, right?

Main question is, as there's a drain cock below the lock shield valve (NB it's not an integrated/one piece drain cock/valve - see photo) is there a quicker way to drain this rad that avoids draining the whole system? E.g. TRV off, lockshield open + drain cock then open?

I'm comfortable with individually isolating and draining this rad but as it's got 20 L of water inside it will take ages.

So just wondering what the best method is that balances speed with faff and avoiding more inhibitor, if possible.

Helpful feedback is very welcome, thanks

 

[Timmy D]

You need to determine if the leak is from the rad valve tail into extension joint or from the 3/4 union to valve joint.

If extension joint, close both valves, put rubble sack under rad side of valve and loosen union, drain rad. Redo joint and install, open valves to refill.

If union, might just need a little tighten. Try a tighten first, wont need to drain anything.

 

[LogicalLarry]

Thanks Timmy, I’ll try tightening the union first but pretty sure it’s between extension and tail.
No draining short cuts given the position of the drain cock?

 

[Ben-gee]

No because if you shut the valves - the drain cock is on the system side of the valve , not the radiator side.

 

[LogicalLarry]

No because if you shut the valves - the drain cock is on the system side of the valve , not the radiator side.

Makes sense, thanks for clarifying. How many turns of PTFE would you put on the tail/extension junction?

 

[ShaunCorbs]

20 -24

 

[LogicalLarry]

20 -24

Thanks a lot, put lots more turns on + some jointing compound and touch wood all seems ok now.

Thanks + to all who helped.