Central heating air bleeding question

Dutch Guy · 9 Feb 2011 at 09:56

We have a central heating system in our house with oldish radiators.
As I understand once in a while these have to be serviced by bleeding out the collected air.
But should I do that when the central heating is off or should I bleed the air when the system is heating and running?

Brian8bit · 9 Feb 2011 at 09:57

I do it when the heating is running.

Schizo · 9 Feb 2011 at 09:57

on and running

Bossk128 · 9 Feb 2011 at 09:58

Do it when the system is on and hot. Any radiators that do need bleeding will have a hot bottom (oo er!) and a cooler top where the air is. Sometimes you can use a screwdriver, sometimes a special tool is needed depending on the radiator. Turn the release valve until you hear air hissing out, stop when water comes out - it's a tiny amount.

Also,start downstairs.

yhack · 9 Feb 2011 at 09:59

Turn the heating on and try and bleed all the radiators before they get hot, it's a race against time.

Wiggins · 9 Feb 2011 at 09:59

Switch system off first as it can introduce more air into the system.

If all your radiators are hot when the central heating is on then there is no need to bleed them.

A little handymans info here

dekez · 9 Feb 2011 at 10:01

Quick google says to do it whilst the heating is off?

I've never really paid attention to if they are off or on so I don't think it's the end of the world either way. If there is a lot of air released you may need to top your boiler up.

Haze · 9 Feb 2011 at 10:04

if u do it when its off theres no pressure in the system to push the air out !

if u do it when they r hot the will be full of hot air/steam/water and u will scold your self

so use a bit of common sence

Cosimo · 9 Feb 2011 at 10:04

On, running (the pump) and a few turns of the key.

Dutch Guy · 9 Feb 2011 at 10:07

Just as I suspected, half the people say on and half the people say off

I think I will do it as the system is running but not yet hot.

dekez · 9 Feb 2011 at 10:07

http://www.ultimatehandyman.co.uk/bleeding_a_radiator.htm

http://www.diydata.com/problem/central_heating/bleed.php

http://www.diybasics.co.uk/HowToBleedRadiator.html

All say to do it with the heating off. The system is under pressure anyway so it doesn't matter if it's off or on.

edit: just noticed your location, central heating systems may be different in the Netherlands!

a1ex2001 · 9 Feb 2011 at 10:18

The system is under pressure regardless of wether it is on or off so I would suggest doing it while it is off, this avoids the risk of a face full of boiling hot water and in the event you get it badly wrong wrecking the boiler by dropping the pressure to far.

Duke · 9 Feb 2011 at 10:19

Our plumber said do it when the system is off, else it could draw in more air again.

Dutch Guy · 9 Feb 2011 at 10:40

dekez said:
edit: just noticed your location, central heating systems may be different in the Netherlands!

I lookad at the youtube vid in your first link and our radiator is almost the same so I guess it will be fine.

I will do it when the system is off and see how it goes.

I will also feel the radiators to get an idea how hot or cold they are at the top.

a1ex2001 · 9 Feb 2011 at 11:45

Dutch Guy said:
I lookad at the youtube vid in your first link and our radiator is almost the same so I guess it will be fine.

I will do it when the system is off and see how it goes.

I will also feel the radiators to get an idea how hot or cold they are at the top.

Don't bother with feeling the radiators just go round and bleed the lot, if air comes out keep going until you get water if only water comes out close the valve. Job Done.

I say this because you will have to visit each radiator to decide if they are hot enough or not, only a really bad one will ever be cold as the metal they are made of is a very good conductor of heat! So you might as well just bleed them while you are there which will have the added bonus of stopping the bleed valves from seazing solid.

Dandle · 9 Feb 2011 at 11:48

Haze said:
if u do it when its off theres no pressure in the system to push the air out !

The system always has pressure, its mavity fed from the header tank (unless its a pressurised system, which will have even more pressure). Radiators should be bled with the system turned off, the air will collect in the top of the rad over time and just sit there until its bled out. As other have said bleeding with the system on doesnt help and can suck air in. Makes no difference if the rads are hot or cold either apart from the risk of burning hot water if they have been on.

aln · 9 Feb 2011 at 11:59

If you do it when its on, you'll likely be pulling more air into the system. Turn it off, and start from the furtherst away afaik. Your pressure may drop whilst doing this, so you might want to add some more water to the system when done.

TwsT · 9 Feb 2011 at 12:04

put your hand on teh cold part of the radiator and when it gets warm close the valve a bit then a bit more till closed, shoudl stop any spills

meghatronic · 9 Feb 2011 at 12:06

TwsT said:
put your hand on teh cold part of the radiator and when it gets warm close the valve a bit then a bit more till closed, shoudl stop any spills

jas72 · 9 Feb 2011 at 12:11

I have the opposite problem to yours my rads are cold at the bottom

Also the trapped air can still be present in the boiler itself which might need blead by a maintenance engineer/plumber.