Adding an expansion vessel to central heating system

GDB2222

If I need to add an expansion vessel to an existing central heating system, can I do that without draining the system? 

I was thinking of one of those self cutting taps, like this
https://www.screwfix.com/p/self-cutting-isolating-valve-15mm/59752

Then just attach the new expansion vessel.

ThisIsWeird

Yes, you can. With all the normal provisos for these self-cutting devices. The main one being, will the half-cut disc (a copper 'chad'?!) partially block the pipe?

I understand the EV should go on the 'return' side of your CH.

What's the problem? Is it a sealed system? If so, it should be much easier to fit - far less water loss - even doing it 'properly'! You could isolate the boiler, so only have the water in the rad system to deal with. In practice, once it's been depressurised, the water will usually come out very slowly and only in easy-to-stop slugs, as air needs to go the same opening in order to replace the water glugging out. A few things ready to hand - a simple plug or denso tape to cover the cut pipe ends whilst you get the fittings together - and bob's your mildly damp uncle.

plumb1_2

GDB2222 said:

If I need to add an expansion vessel to an existing central heating system, can I do that without draining the system? 

I was thinking of one of those self cutting taps, like this
https://www.screwfix.com/p/self-cutting-isolating-valve-15mm/59752

Then just attach the new expansion vessel.

No, because any small bits of copper could circulate around your system and damage any number of parts.

GDB2222

Yes, I did wonder about the debris from the self cutter getting into the system. 

Oh well!

grumbler

Not sure if you can control this, but in this case the flow through the hole is minuscule, so it can work if you stop early before cutting the full circle so that the round bit remains in place.

ThisIsWeird

grumbler said:

Not sure if you can control this, but in this case the flow through the hole is minuscule, so it can work if you stop early before cutting the full circle so that the round bit remains in place.

Interesting idea. So you'd leave the fitting's tap open during the cut, and stop cutting the moment a trickle comes out?

Sounds like a good plan IF you really must use one of these.