How to Bleed Radiators

Bleeding a radiator means releasing air that has become trapped inside your heating system. Letting this air out will help you to heat your home more effectively and reduce your energy bills. If you can hear pipes banging or radiators gurgling, this is usually a sign that you should bleed your radiator.

You will need –

TURN THE HEATING OFF AND ALLOW IT TO COOL DOWN

It is important to turn the heating off and allow the radiators time to cool. This is to make sure that the hot water in the radiators doesn’t burn you when you start to bleed the radiators.

This is also very important because some water pumps – depending on where in the system they are fitted – will actually suck more air into the radiator and consequently the heating system if they are turned on while you open the bleed valve.

FIND THE FIRST RADIATOR TO BLEED

If several radiators require bleeding there is a logical order in which to bleed them. Air rises to the top of the system so it is best to start at the lowest radiators that you have and work upwards.

If your home has 2 floors you should begin bleeding the downstairs radiators first. Start with the radiator furthest from the boiler if there are several on the same floor or level and slowly work in towards the boiler. Once you’ve bled all the downstairs radiators you move on to the upstairs, again beginning with the radiator which is furthest from the boiler.

BLEED THE RADIATORS

  1. You will usually be able to find the bleed valve at the top and side of your radiator.
  2. Put your container or towel on the floor beneath the bleed valve.
  3. Take your radiator bleed key and insert it into the bleed valve until they have locked together. Hold your cloth next to the valve and under the little drain hole and be ready to catch any drips.
  4. Slowly turn the key anti-clockwise to open the valve. This will allow the air to escape and you should start to hear a hissing sound. Keep turning the valve until it is a quarter to a half of the way open. Make sure to not open the valve to fully to avoid water escaping too quickly.
  5. Once the hissing noise and air stop – and water starts to leak out – you will have bled all the trapped air from the radiator.
  6. Turn the key clockwise to close the valve. Make sure not to close the valve too tightly to avoid damaging the valve.
  7. Bleed any other radiators

CHECK THE BOILER PRESSURE?

If you have a pressurized central heating system you may notice that the pressure gauge on your boiler has dropped since bleeding your radiators.

Your boiler must be at just the right operating pressure for your heating to work properly. If the boiler loses pressure or if the pressure is too high this may cause your boiler to shut down or ‘lockout’.

WHAT SHOULD THE BOILER PRESSURE BE WHEN THE HEATING IS ON?

When the heating is turned on your boiler pressure should be between 1.5 and 2 bar.

Most boilers will highlight this area on the pressure gauge in green to help you see if the needle is pointing to the correct amount of pressure.

Some boilers will also have the critical zones below 1 and above 2 marked in red to help you identify any issues.

WHAT SHOULD THE BOILER PRESSURE BE WHEN THE HEATING IS OFF?

If your central heating system is turned off the boiler pressure should be between 1 and 1.5 bar. This means that the needle should still stay in the green area of the pressure gauge.

Depending on the make of your boiler, the recommended optimal working pressure by most manufacturers is 1.3 bar.

It’s a good idea to keep an eye on the boiler pressure just before the heating season starts so that your boiler is in top shape for winter.

How do I increase the pressure on my boiler?

Locate the filling loop. Open both valves to allow water into your heating system. Keep an eye on the pressure gauge and close the valves when the pressure reaches 1.5 bar. Switch on your boiler and reset the fault code (if necessary).

Our Weil-Mclain Boiler

Pressure/temperature gauge or pressure gauge (steam)

Water boilers — Make sure the pressure reading on the boiler pressure/temperature gauge does not exceed 24 psig. Higher pressure may indicate a problem with the expansion tank or gauge.

When the boiler is COLD, the pressure should sit around 12-15 and go UP when it fires and the water is heated. The top curve on the gauge is the one to look at, not the one that curves around the bottom of the gauge. The number to look at on the top curve is the one inside of the curve, not the one on top of it.

For our Weil-Mclain Boiler, there is a valve on the water pipe to the left of the boiler going over to the water tank in the ceiling. Open this to let more water in until the pressure reaches the desired pressure.

We were not getting any air or water when bleeding our radiators on the second floor and found that our the pressure on our boiler was too low, We opened ours until the pressure was 18 psig. Our radiators were then getting hot to the top and we got a bit of air, but no water. The number to look at is INSIDE the curve (the higher numbers), not the one on top of the curve. We were looking at the number on top of the curve and the water was not filling all the way. A heating and cooling contractor told me about this.

New Water expansion tank, Auto fill and back flow preventer, and Air separator

Auto fill and back flow preventer - new valve next to the shut off valve for the water line coming into the furnace. Leave the shut-off valve off unless more pressure is needed in the boiler. The valve is on when the handle is parallel to the pipe, and off when the handle is perpendicular to the pipe.

An "Autofill" is a device that automatically adds water to a system to maintain a set pressure level, while a "backflow preventer" is a mechanism that prevents contaminated water from flowing back into the clean water supply, essentially only allowing water to flow in one direction.

*** The Auto Fill valve is set to 15 PSI and will turn on if water is needed in the furnace. With the regular water shut-off valve closed, it will not fill though. If the PSI pressure on the furnace is too low, open the water shut-off valve. The Auto fill and back flow preventer will automatically fill until it gets back to 15 PSI and then will not let in any more water. If water is added, you should also open the Air separator and wait a day before closing.

Air separator - device that sits on top of the new expansion tank

Air separators are used to eliminate air efficiently and quickly from the piping system in closed loop heating and cooling applications. Air separators work by creating a low-velocity, low-pressure zone where water slows down and bubbles coalesce. The bubbles then rise to the top of the air separator and are expelled from the system In a worst case scenario, a malfunctioning air separator could literally cause a no-heat situation.

Air develops in the system as a result of the water it contains expanding and contracting as it heats up and cools down during normal operation. If you hear funny gurgling or bubbling noises coming from inside the boiler or the piping and heaters, trapped air in the system could be the culprit. An air separator is built to remove errant air that runs around inside your boiler system, potentially creating noise and trying to make bigger waves for your home comfort.

If water is added to the heater to raise the PSI level, this should be opened, left for a day, then closed again.