How do you drain a central heating system

[Joeylegend]

Need to put in a new radiator in the bathroom.

Need to take the old one out and put a new one in. All the existing pipework will need changed/moved to cater for the new position of the new rad.

How do you drain a central heating system? Is there an easy way or shortcut to draining every rad in the house?

 

[Softus]

How do you drain a central heating system?

Firstly, fit a hose with a jubillee clip over the nozzle of a drain off cock.

Then it depends, slightly, on whether you have an open-vented system or a combi.

If a combi then just drain. If not, then isolate the supply to the F&E cistern to prevent more water entering the system, and then drain.

Is there an easy way or shortcut to draining every rad in the house?

You don't necessarily have to drain every rad. For example, if the bathroom is upstairs then you don't have to drain the downstairs rads. However, for each rad that you do want to drain, open its vent so that air is allowed in to replace the exiting water.

The hardest part you might face is getting all of the water out of the pipework that you want to modify. If you're soldering then you have to get the water area from where you're soldering. Consider compression and/or push-fit options, because this immediately solves that problem.

Advice:

1. Replace the washer on the drain cock that you use to drain, before refilling.

2. Ensure that you add enough chemical inhibitor when refilling.

 

[Joeylegend]

Thanks for this advice softus, where would I find this ‘drain off cock’?

The rad is in an upstairs bathroom, a pipe from the old rad appears to go strait up and into the roof space to the little C/H water tank. Therefore I think this means this rad is the first or last on the system.

It is not a combi C/H system

 

[Softus]

Thanks for this advice softus, where would I find this ‘drain off cock’?

Could be anywhere. Commonly on a pipe near a radiator, but also frequently found outside at a level near the DPC.

Looks like this:

The rad is in an upstairs bathroom, a pipe from the old rad appears to go strait up and into the roof space to the little C/H water tank.

That would be unusual, and I haven't yet managed to think of a reason why it would be piped like that.