Add a rad to a combi system

[richplumb]

I want to add a small radiator downstairs to a combi boiler system.
Do I need to drain the whole system or could I get away with simply relieving the system pressure and closing all radiator valves?

[MANDATE]

It's best to make sure the pipes you are cutting into are free from water,
so you'll have to drain it off from the pipe work, Closing off all radiators Is optional, but is it worth it when you will have balance the whole system. Might as well drain and refill them and bleed them,m easier and quicker.

[namsag]

As a diyer it will be far easier to just drain a pressurised combi system as they usually empty and fill quite quickly. But there is a way of doing it full, If boiler has half decent isolating valves turn these off then release pressure from system either from a drain cock or a bleed point on a rad when water stops close whatever you have used. When you now cut into pipes you will get a minimal amount of water l come out allowing you to connect new pipe work etc even using soldered joints but there is a knack to it.

[sm1thson]

draining also means you get to replace the smelly old water with new stuff (might be worth i diy flush at the same time? -see the wiki), when you add new water dont forget to add inhabiter to keep it fresh!