Replacing radiator air vent valve

[JoeJoe]

After hearing noise from the heating system for the last few days I decided to try and bleed it.

Opened the air vent valve on one of the radiators, and when trying to tighten it back the little screw in the middle snapped…

Photos here:

It is not leaking at the moment as far as I can tell (fingers crossed).

1. Can I simply unscrew what remains of the air vent valve and replace it with something similar to this one?
2. Can it be replaced very quickly without having to empty the system? the radiator is upstairs and I can hold a towel under it. Happt to top it up a little if needed once completed.
3. What size should I buy? They seem to come in 1/8, ¼, ½ inch (possibly others). It is a “standard” domestic radiator. Happy to measure, but not sure how.

Anything else I need to consider?

[SteveW]

Most radiators (unless they have a built-in, non-replaceable bleed valve) use a 1/2" version

That can be replaced, without losing much water, if you close the feed and lockshield valves at either end of the radiator.

Make sure you wrap some PTFE tape around the new valve before screwing it in - and that you wrap it in the right direction, so that it does not just strip off as you screw the valve in.

[JoeJoe]

Many thanks. Will get one tomorrow and have a go.

Any idea how to measure it to make sure it is the right size? What is left attached to the radiator is approx 1cm from side to side ("diameter" - what I can see it not round of course).

(was going to use PTFE, I swear... and am aware of the importnace of wrapping it the right way around).

[John Rumm]

1/2" BSP is about 19mm across the threads - so a bit more across the flange of a fitting.

(the 1/2" is the nominal *internal* diameter of a thick walled iron pipe)

[JoeJoe]

Thanks.

Mine looks very much like a 1cm in diameter to me, or close to it (see

Does it mean that I need to get the 1/4"" valve, not the 1/2"?

[John Rumm]

That does not look like a "standard" 1/2" BSP radiator bleed valve fitting. A 1/4" BPS fitting is about 13mm diameter across the threads - again I suspect not what you need.

You might have a Myson radiator - they have a rather different bleed valve arrangement:

or:

[Mike Clarke]

With the radiator's inlet and outlet valves firmly shut off you can remove the body of the old bleed valve and take it with you to a plumbers merchant to get one that matches up.

But if you have a TRV remove the head and use a decorators cap to make sure it won't open if things get colder or put the head back on with a

5p piece under it to ensure a more positive shut off.

[JoeJoe]

Had a look at the radiator - was fitted with another 7-8 during a renovation around 15 years ago - but couldn't work out the maker.

It there a way to do that/somewhere to look? The Myson rings a bell, but I cannot be sure that it was what was fitted.

[JoeJoe]

How do I shut off the side with thermostat? Simply tun it to 0?

[Rob Morley]

"But if you have a TRV remove the head and use a decorators cap to make sure it won't open if things get colder or put the head back on with a

5p piece under it to ensure a more positive shut off."

[John Rumm]

The style of the one you posted a pic of looks like a Myson, and the diameter of the plug looks about right as well.

No doubt google will find you plenty more piccies to compare against.

[JoeJoe]

Thanks a lot.

It does indeed look like a Myson in the photos that I found.

Will place an order tomorrow.

[Roger Mills]

Good advice.

Looking at the photo in the OP, my guess is that it's probably 1/8" BSP

- which has a male thread diameter of about 9.5mm. [As with all BSP fittings, the stated size is the nominal bore of a threaded iron pipe - so the OD is a lot bigger than the stated size.] It is definitely *not* 1/2" BSP, which has a male thread diameter of just over 20 mm.

[JoeJoe]

[JoeJoe]

Thanks again.

Since it doesn't seem clear which valve I need to replace the damaged one, and that the damaged one doesn't seem to leak, I think that I will probably leave it until after xmas when the house is going to have less occupants....

I'll just get 1/8, 1/4 and a myson valve and try until one fits. They only cost a couple of pounds each.