Radiator tails and sizes

[milkman]

Advice needed before I take this thing apart. Is the fitting for tails standard or is it common for new valve tails not to be able to fit into a radiator?

My new TRVs come with 15 mm tails and the existing ones are I think 3/4". Whatever they are they're bigger than 15mm.

Also the existing tails don't appear to have that hex key shape on the inside to allow you to take them out. Thoughts and observations welcome.

2nd question:
I've read that you can undo a valve on a sealed central heating system and provided no other parts of the system are open the vacuum will prevent too much leakage.
If its a pressurised combi type how much pressure do you need to let off beforehand? All of it or a bit? [our system is normally about 1 bar or just over]


Thanks in advance
Marko[/i]

 

[Trundles Tricks]

Threads are in imperial sizes and will be a standard 1/2 inch not 15mm, it is unlikely that any domestic radiators will have a larger size than this, if this is the case it is likely to be 3/4 inch and you can bush it down to 1/2 inch, all current standard Rad valve tails will fit the smaller size.

No Hex? You'll just have to use grips or pipe wrench on the tail (cutting off union if necessary to get a decent grip.




Any domestic radiator with a connection larger than 1/2 inch is likely to be quite old and I would recommend a thorough inspection and possible replacement if required.


I'd drain down if I was you, whilst the adrenaline rush of a face full of water followed by a full scale flood can prove invigorating to some, in general it's best to be avoided.

 

[bengasman]

Your existing tails are probably the ones that have 2 little points inside. Could be 20 years old and might be very stuck, takes a special tool to get them out.

 

[Biggles..]

without using a hex key or rachet spanner for rad valves sometimes the best way is to

Remove the radiator, remove valves from pipework, tighten valves back on to radiator tails(very tight) and then using the valve body unscrew from whole lot from rad.

Lee