Creating a vacuum on CH pipe runs.

[WaterTight]

I do this regularly to change a leaky/broken radiator valve, usually without issue.

Sometimes I do this to change a rad, even if changing valves / altering pipework, do one side at a time, usually without issue but sometimes (especially if piped on drops it seems) get air problems.

My question is ...for the latter, and perhaps especially on drops, is doing this more likely to get air in system then just draining fully down and refilling methodically? I used to just drain down but started doing it this way a few years back as imagined it would not only be quicker but disturb the system less and so maybe make problems like air less likely. But I'm not sure what I was basing it on.

Recently done a few rad changes on drops via this method and get lots of air to persuade out. Wondering if should just go back to drain downs.

Cheers

 

[oz-plumber]

The vacuum method is hit and miss at times.

If you're comfortable doing it, then keep doing it.
Nothing is infallible, so you are always going to end up with some problems

 

[WaterTight]

Do you think if the rad is piped up on drops that doing the vacuum method is more likely to get air locks on refill than a drain down?

 

[king of pipes]

I wouldn't say so drops have a habit of locking up you simply turn off the rads that get hot and it usually clears it , I use your method sometimes it can be a bit challenging . Kop