CH Boiler Drain cock

[suffolk]

Below my Boiler I have a Pressure Relief Valve which vents to the outside and a drain cock (see image)
The drain-cock is dripping and requires a new washer
If I release this drain cock
Will it just drain down until the Expansion Tank pressure drops to 0bar until no more water flows
Or
Will it drain down the entire CH system ( my worst nightmare)

 

[ShaunCorbs]

It will drain the entire heating primary system

 

[suffolk]

Blast, thats what I thought, alot of hassle to stop a drip
I will try a can of Pipe Freeze in the 15mm pipe above

 

[Timmy D]

Drain the pressure to zero. Put bucket under drain cock. Close boiler isolation valves.

Whip out the spindle and washer. Quickly refit.

For a bit more time, get a second pair of hands to put the fingers over the drain cock outlets while to attach the new washer.

 

[suffolk]

I have been succesfull. I have no isolation valves on the boiler
I closed both valves eitherside of the pump and released the drain cock
Water drained until ZeroBar and then stopped - Pipe dry
Changed tap with no problem,

Thanks for your advice