draining system

[AndyBill]

hi,
i have a combi boiler and need to drain the central heating system down,
can anyone advise on the best way to do this ?

does it matter which downstairs rad you drain from?

how do i prevent air lock?

cheers

 

[gas4you]

Turn boiler off and drain from lowest drain off. Open air vents in rads starting with upstairs then downstairs when the water has drained below air vent level.

Don't forget to add new inhibitor when re-filling system

 

[AndyBill]

thanks for that,

do i need to turn the water off at the stopcock or anything?

i think all my downstairs rads are about the same level,
so can i drain from any of these?

cheers

 

[gas4you]

No. As it is a combi it is only connected to the cold mains by its own filling loop, whether it is a serperate loop or maybe built in combi depending which make you have.

Any rad will do

 

[AndyBill]

thanks for the help

 

[AndyBill]

how do you fill it back up again?

do you bleed air out as they are filling?

 

[gas4you]

You need to add inhibitor to the system first, possibly via a radiator, then pressurise your combi to around 1.5 bar then go to each radiator and let then bleed from air vent. You may find this stops after a few radiators, so go back to boiler and re-pressurise again this time only to about 1 bar and repeat process.

What boiler do you have? When you first turn boiler on set thermostat to low setting. Boiler will be noisy at first then quieten as air is pushed around. Then go around rads again after about 30 mins to bleed again. Check rads again after about 1 week or if any are cold at top

 

[AndyBill]

its a Vaillant combi.
is there any chance of me blowing the boiler up if i do it wrong is there?

 

[gas4you]

If it is a new ecotec plus then you have to let the boiler purge the heating system via the built in program. If an older model then it should be ok