Do I really need to drain the system

[JarraDIY]

I am upgrading to a Type 22 radiator in my kitchen as I'm now working from my kitchen table and it's never quite warm enough in here.
I have an old micro bore system, and having seen a plumber convert an upstairs radiator to type 22 I am confident of being able to do this myself in the kitchen.

My query regards draining the system. The kitchen radiator sits lower than my combi boiler (which is also in the kitchen).

Is it really necessary to drain the whole system from top to bottom?

I realise the rad itself will contain water but if I don't open any bleed valves in the upstairs rads, and release pressure via the combi boiler, will I be able to remove the radiator and original valves without water continuing to flow from the pipework?

Obviously I know about gravity but the trick of putting a hole in a plastic water bottle and water not running out comes to mind.

I am also concerned about how to introduce rust inhibitors if I drain everything completely.

Thank you in advance.

 

[Ben-gee]

As long as you only have one open end at any one time , yes you can do it.
It will hold on a vacuum, if however you have two open ends one will let air in and therefore water out of the other one and you’ll very quickly be in big trouble!
I do it like this all the time to save draining down/refilling.
If you choose your rad size carefully and there is enough play , as it’s microbore- you may well not need to alter the pipes anyway, just ease them into place and reconnect to the new rad.

 

[Scott_D]

How do you plan to release pressure at the boiler?

 

[Ben-gee]

To OP, release pressure via drain off, not at boiler .
If no drain off then release at the rad you are removing.
I noticed you plan to replace valves ( is that necessary?), if so do them one at a time- with the other one shut off.

The way in which this method can get you into trouble is if there is an unknown (to you) source of air release on the system - this is usually an automatic air vent and they can be found at any point on a system. If there is one you can find that suddenly the whole system is emptying through the pipe you are holding!
If you are not prepared for this and don’t know what to do should it happen - you are better off draining the system.

 

[Ric2013]

I am also concerned about how to introduce rust inhibitors if I drain everything completely.

Easy. Either buy the pressurised type that you squirt into a radiator bleed valve, or use whatever you can cobble together to pour into one of the top tappings of the new radiator before you fill it entirely after fitting. Then run the system to put the inhibitor into circulation.

Technically speaking you should probably still flush the system with a new system cleansing agent to remove any manufacturing oils from the new radiator, but unlikely anyone would go to those lengths as customers usually unwilling to pay. Depends how new and shiny your boiler is, I suppose.

 

[JarraDIY]

Thanks everyone for the advise. It's obvious now the plumber who fitted my vcombi and 1 year later a new rad for me didn't use an inhibitor.
I have posted a pic if the current valve, so you can see why it has to go. Looks crap and sometimes decides to leak.
I am converting from 8mm microbore to 10mm pipework and modern 10mm valves with shiny new rad.... hopefully this coming week.

 

[JarraDIY]

Looking at the valve, can anyone advise how the heck I drain the system? All the downstairs rads are the same, no drain facility. I am even willng to get a wet vac but there is nowhere to attach it!