Lockshield valve

Try draining at a lower point in property...if cant use a wet vac to collect excess water fowm heating system

Yes — what you’re missing is that draining the radiator does not drain the heating pipework.

If water is still rising from the pipe coming up from the floor into the lockshield, that usually means the heating system still has water in that circuit, so the pipe is still live. The radiator may be empty, but the flow or return pipe below the valve is still full of system water.

Common reasons:

1. You have only drained the radiator, not the system or that branch

Closing the valves and emptying the radiator only removes water from the radiator body.
The pipe feeding the lockshield can still contain water from the rest of the central heating system.

2. The system is sealed and still under pressure

If it is a combi or sealed heating system, water can still be pushed up the pipe by system pressure unless the heating circuit is fully isolated and depressurised.

3. Water is being held in the vertical pipe and surrounding circuit

Even with pressure off, there may still be a lot of residual water in the pipework above and below that point.

4. The valve may be on the return side of an active circuit

If other parts of the system are still full, disconnecting that pipe end can release a surprising amount of dirty heating water.

What you normally need to do before replacing the valve properly:

Turn the boiler off
Isolate the filling loop if it is a sealed system
Reduce heating system pressure to zero
Drain the heating system down to below the level of that valve, not just the radiator
Keep towels, tray, wet vac, and caps/freezing kit ready if you are working locally

In some cases, plumbers use:

a pipe freezing kit for a local valve swap
or a full/partial drain-down of the heating circuit

Also, just to note:

PTFE tape will not normally fix a leaking valve body or spindle leak
If the leak is from the gland/spindle, sometimes the gland nut can be tightened slightly
If the leak is from the valve body or compression joint, replacement is usually the proper fix

Because draining the radiator doesn’t drain/isolate the heating circuit. The pipe side is still connected to the rest of the system, so water will keep feeding it (by gravity from higher pipework, or because the system is still pressurised / being topped up).

What to do :
• Turn boiler off.
• If combi/sealed system: isolate the filling loop and drop pressure to 0 bar by draining from a low drain-off/rad.
• Close both rad valves (TRV + lockshield) and open the bleed to break vacuum.
• If it’s an open-vented system: you may need to bung the feed & vent in the tank/loft and drain enough water down.

If you don’t fully drain/isolate the circuit, cracking the valve off the pipe will dump system water onto the floor

This is common situation.
Turn off boiler and isolate system.
Water will be coming by gravity.
Solution, use plastic deep tray or bucket for draining water.
Replace valve.

Your heating system is still under pressure, you would need to drain down the radiator system and the radiator with said issue, remove said lock shield replace with new, reconnect the radiator (add some inhibitor if needed) and refill the system bleeding the radiators to expel the air

System Pressure: If you have a sealed system (common with combi boilers), there is stored pressure throughout the entire circuit. Even after draining one radiator, the rest of the system will push water toward any open outlet.

To replace the lockshield valve safely, you either need to: fully drain the heating system at the lowest drain-off point, use a pipe-freezing kit to temporarily block water in the pipe, or close isolation valves (if fitted). Without one of these methods you’ll get a continuous flow of water when undoing the pipework, which is why it looks like it’s still “filling up” even though the radiator is empty.