What are my chances of freezing this?

[GB]

I want to replace the cartridge in the 3 way valve on my GCH. That's a lot easier than replacing the whole mechanical part of the valve. The obvious thing to do is to drain the whole system down, do the job, then refill. But it's a big system. 2 litres of Fernox, plus the time.

The valve is 28mm. I have good access to the 3 pipes coming in. What chance of a successful freeze job? Replacing the cartridge will only take a minute, btw.

BTW, on other systems where I've topped up the Fernox, I've opened up a joint and poured it in with a funnel. Is there any good way of pushing it in through the drain valve? I'm obviously being particularly wimpy today. :)

[Jethro]

The bathroom ladder-type radiators are great for this ... just take blanking plug off and fill ...

[Dave Liquorice]

Donno on the shed based aerosol can things, see if they give a max pipe size on the destructions?

What sort of system is is open vented or pressureised? With open vented you can block the vent and cold feed and take a rad valve out with minimal spillage but that is only having two open pipes at the same level more or less. As air can't get in the water can't get out...

You might be able to get the same result with a 3 port valve if you can stop water moving around the pipe work by closing valves. One end of *every* rad (beware of thermostatic one opening, take the head off and use the mainentance cap), pump isolation valves etc. 28 mm may well just glug though...