isolate radiator change to change leaking valve?

[gb17342]

Hi all, I need to replace this valve as it's dripping even when turned off so presume its old and worn out. How do I isolate the water supply to it? When I open it slightly water comes out a lot so if I take the valve off completely to replace it do I just need to quickly get the new one on and tightened up or is there an isolation valve on the supply from the boiler? I've added a picture of the valve and the pipes under the boiler any advice is greatly appreciated.
PS. the water isn't leaking from the nut and olive on the pipe it's dripping out where the valve connects to the radiator.

 

[steadyon]

1. Its not unusual for radiator valves to fail to shut off completely.
2. If it doesn't leak when the radiator is connected I'd leave it alone.
3. You have a combi boiler, and hence a pressurised central heating system. You could:
3a. Turn the boiler off.
3b. Shut off the flow and return to the system. This is done by turning the black plastic handled valves on the 22 mm pipe to left and right of underside of boiler.
3c. Release pressure from the system via. the bleed point on another radiator. You'll need something to catch the water. Shut the bleed point.
3d. Open the valve you are going to change, running excess water into a bucket / pan. The flow should stop after a short time as you have effectively created a vacuum in the system. If it doesn't stop, then there is another open point in the system.
3e. Change the valve. Old towels down to catch water / black sludge. Note that your valve is what is known as a union type. Unless you want to change the tail in the radiator, get a replacement of a different sort.
4. The alternatives, which might be safer depending on your level of expertise:
4a. Isolate flow and return, then drain the system down completely.
4b. Freeze the pipe leading to the valve to be replaced.

 

[gb17342]

1. Its not unusual for radiator valves to fail to shut off completely.
2. If it doesn't leak when the radiator is connected I'd leave it alone.
3. You have a combi boiler, and hence a pressurised central heating system. You could:
3a. Turn the boiler off.
3b. Shut off the flow and return to the system. This is done by turning the black plastic handled valves on the 22 mm pipe to left and right of underside of boiler.
3c. Release pressure from the system via. the bleed point on another radiator. You'll need something to catch the water. Shut the bleed point.
3d. Open the valve you are going to change, running excess water into a bucket / pan. The flow should stop after a short time as you have effectively created a vacuum in the system. If it doesn't stop, then there is another open point in the system.
3e. Change the valve. Old towels down to catch water / black sludge. Note that your valve is what is known as a union type. Unless you want to change the tail in the radiator, get a replacement of a different sort.
4. The alternatives, which might be safer depending on your level of expertise:
4a. Isolate flow and return, then drain the system down completely.
4b. Freeze the pipe leading to the valve to be replaced.

That's extremely helpful thank you steadyon. It only leaked when I disconnected the shut valve, it was no problem when connected to radiator so I will just re-attach once I've re-decorated. However, when you say it's a union type valve why could I not replace with a similar valve? I found a similar one in screwfix for a few quid looks the same I presume that's also a union valve, figured I could just undo the nut and switch them over, why would I need to replace the radiator tails if I used the same type valve? If a different sort would I use a thermostatic valve? Many thanks again for your help

 

[Gasmk1]

because the thread size and union nut might be different so not interchangeable you may have to swap the whole valve including the tail in the rad

 

[gb17342]

because the thread size and union nut might be different so not interchangeable you may have to swap the whole valve including the tail in the rad

I see, thank you

 

[steadyon]

Sorry, my post should have read "... of the same sort", not different.