LOW
SYSTEM PRESSURE?
AIR IN SYSTEM?
How To Re-Pressurise a Central Heating System and Bleed the Radiators:
To
keep your boiler working efficiently, it is essential that any air that
has found its way into the system be removed or 'bled' from the
radiators. Common symptoms of excess air are:
You
will first need to establish if you have pressurised central heating.
All combination boilers are pressurised, as are some conventional
systems. A pressurised
system will have a pressure gauge which is usually located on the boiler
facia however some models have the pressure gauge on the bottom, these
will need to be viewed from below the boiler. This gauge will be graduated in 'bars' and
should read between 0.8 and 1.5 bar (usually 1 bar) when the system is
cold. Gradual loss of
pressure is normal.
If
your system is conventional and you have a feed and expansion tank
(central heating header tank) your system will be topped up
automatically and you will only need to bleed the radiators as detailed
below.
If
your system is pressurised, you should regularly check the pressure
gauge and top it up if necessary.
Pressure
is increased by adding water from your cold water main. There will be a
device called a filling loop/valve somewhere on the system. The filling loop/valve
will usually be a flexible connection below the boiler (see Fig.1) but
in some cases this is an integral part of the boiler (see Fig.2) or, it
can be located behind the washing machine, in an airing cupboard or
under the kitchen sink. If in doubt, consult your boiler installation
instructions or your installer.
Open
the valve or valves on the filling loop whilst watching the pressure
gauge.
Water
can usually be heard moving into the system. Do not over
pressurise -
it is easier to put it in than to take it out!
When the gauge shows the correct pressure, turn off the valve or valves
and bleed the radiators as detailed below.
Constantly check the pressure level at the gauge and top up when
necessary, until all radiators have been bled of excess air.
Finally, ensure that the pressure reading is correct and that the filling
loop valve/valves are closed.
To
Bleed a Radiator:
You will need a
bleed key (available from any hardware store) and an absorbent
cloth/tissue.
If
the central heating is on, turn it off and wait until it has cooled down
enough - a central heating system is filled with hot and sometimes
extremely dirty water so precautions should be taken to protect floor
coverings and decorations.
Start
with the lowest radiator on the system and work towards the top. Some
hot water cylinders also need to be bled.
Holding a cloth to catch any water spillage, slowly and gradually
loosen the bleed screw on the radiator (do NOT remove the bleed screw)
until any air (evidenced by hissing) or water starts to dribble out.
If there is no air in the system water will appear immediately.
Close the bleed screw - do not over tighten.
Finally, ensure
that the pressure reading is correct and that the filling loop valve is
closed.
Regularly
check the pressure level at the gauge and top up when necessary.
If your radiators are still cold/cool (especially at
the bottom), or the water in your system appeared particularly dirty,
your system may need to be power flushed. 
Click here to go to power flushing information.
(Fig.1)
External Filling
Loop
|
(Fig.2)
Integral Filling Valve usually on underside of boiler |
|
