How to drain combi boiler central heating system...

[m4ubs]

One of my radiators leaking, not from the valve fitting but from the pipe. The pipe is 10mm and its bent and now leaking drops. I want to re-solder or repair the pipe. Do i need to drain the whole central heating system or not ? and what is the best and easiest way of doing it please ??? Its a combi boiler system...Any info will be much appreicated. thanks...dont know if it makes a difference but its a radiator upstairs and the combi boiler is in the kitchen.

 

[Goldspoon]

I've only drained/refilled twice now on two different combi systems so not an expert but all went okay.

Turn boiler off (ideally at fused spur and remove fuse if anybody about who might switch it on again whilst you messing with rad).

Fix hosepipe to a drain pipe on one of the downstairs rads (or might be a drain off point near boiler) and drain off an amount of water to outside drain or garden (you'll see combi boiler pressure drop from whatever it is, likely between 1 bar and 2 bar... to zero). Keep draining until you have emptied the upstairs rads* (you will need to open the air bleed screw in the rad concerned to allow air in, which in turn allows water out the hosepipe - essentially you are getting rid of a vaccum that would otherwise prevent draining).

*How one knows when you have drained enough water to be below the level of the upstairs rads I am not sure? Any tips? I did one this morning (changed TRV upstairs so drained to just below upstairs rads) but I guessed that enough drained out and it had (removing TRV slowly to see what is still in rad is a bit traumatic though).

With regard to going any further... sounds like you know what you are doing regarding the actual repair of the pipe? You say "re-solder"... what is the fitting that is leaking?

When re-filling you do this using the combi boiler filling loop (boiler still off). Stop at 1 bar pressure and then bleed upstairs rads... pressure will drop so top up to 1 bar and bleed again. When no air in top rads pressure up the system to what it should be (likely 1 bar to 2 bar - check your boiler manual). You should add some inhibitor as you have drained down some water (add inhibitor whilst drained down, either via pipework at TRV or by taking bleed valve out and putting in top of rad)..

As I said I am not a CH expert in any way... I'm sure somebody will chip in if I am wrong or have missed anything.