replacing lockshield valve and draining considerations

[navnic]

Hi All,

I've looked through the forum but still wasn't quite sure so thought I'd ask, all advice is greatly appreciated!

We removed a radiator to decorate (from a combi boiler CH system). When went to refill the radiator when it was put back, the shaft on the lockshield valve has sheared off and the valve is stuck closed.

We have a new valve, a hose pipe and have watched guides on draining the system to replace the valve. However -

1. we live in a flat and have identified 2 drainage valves - can we use any valve or a particular one to drain the system?
2. The guides say that all valves should be open to drain the system, what do we do if one is stuck closed?
3. I've read that there are chemicals in CH systems - is it necessary to put them back in when we refill the system?

Many thanks

 

[footprints]

Any drain cock as long as it is on the same pipe circuit and lower than the valve you want to work on.

As long as the valve the other end is open the rad should drain.

It's up to you whether you put in inhibitor most people do these days although we never used to worry a well fitted system has very little water loss and so not much corrosion as we don't know how good yours is putting it in is probably best.

 

[flameport]

It is not necessary to drain the entire system just to replace one valve.

 

[footprints]

It is not necessary to drain the entire system just to replace one valve.

Yes certainly but if the OP is not experienced it's simpler to say drain that way they have plenty of time to do the job and don't risk getting caught out if a induced air lock fails

 

[Madrab]

If you live in a flat, all on one level, then I'd close all the rads and then depressurise and drain the system at the one you need to replace the valve at, until the water stops.
Undo old valve and replace with new, open that rad and inhibit to required level then pressurise and bleed the system via that rad.
Once that's bled, bleed the rest and pressurise to 1.5bar, run the system till hot and then recheck for air.