Drain a CH system without a drain valve

[raidwi]

I've found a small leak on an isolator for our CH system (sealed system, no drain valve), so need to drain it ideally (I'll replace the fitting with a new compression isolator).

Any tips on how to do this with the least mess? Needed to get to this job at some point so now is as good a time as any. I'm expecting a lot of sludge as not done this before.

I've read the FAQ but it advised to use the drain valve my system doesn't have

 

[terryplumb]

Where is the leaking isolator ,ground floor ,upstairs etc ?
What floor is the boiler on ?
Is there a drain cock on or near the boiler ?

 

[raidwi]

Where is the leaking isolator ,ground floor ,upstairs etc ?
What floor is the boiler on ?
Is there a drain cock on or near the boiler ?

Under ground floor (am working in the cavity at the moment and spotted it)

Boiler is on ground floor.

No drain cock.

 

[terryplumb]

Sometimes in property's as yours ,a drain cock is fitted below floor level and goes out externally , through brickwork .

 

[raidwi]

Sometimes in property's as yours ,a drain cock is fitted below floor level and goes out externally , through brickwork .

Thanks for the reply.

There isn't a drain going outside for this. Only one is the boiler's PRV drain.

 

[kidgreen61]

As the part you need to replace is under the (I assume suspended floor). just close the isolation valves under the boiler and slacken the leaking fitting until the pressure has dropped, you can then change fitting without draining it all.
You will lose a drop of water, and not have to worry about any mess/damage because the water will spill on concrete slab beneath floor.

 

[oldbuffer]

If you are talking about an ordinary isolation valve (e.g. Screwfix 65251):
1. these should not be fitted to central heating systems. They are generally not rated for the continuous high temperatures of central heating, and will eventually leak.
2. I'd suggest you remove it and replace with a straight piece of pipe.
3. And do the same for any other isolation valves of the same type.