With the winter upon us, many are now opting to turn their radiators on to bring some respite from the cold weather.

However, after so many months of not using them, we may find that they are not working as well as they used to.

For example, we may find that the bottom half of our radiators may be colder when compared to the top half.

Why is the bottom of my radiator cold?

Bury Times: Cold patches on a radiator may be caused by sludge build-up (Getty)Cold patches on a radiator may be caused by sludge build-up (Getty) (Image: Getty)

According to Ideal Heating, one of the main things causing the bottom of a radiator to become colder is the build-up of sludge.

This occurs over time as the radiator's joints and pipework begin to rust. This rust then breaks up into the system and combines with dirt to create a thick, gooey liquid.

How do I prevent the build-up of sludge in my radiator?

The best way to deal with this problem is to prevent the issue from occurring in the first place.

One way to prevent it from becoming a problem in your radiator is the use of a System Filter which can be installed in the loop.

This catches the grime before it has a chance to settle and accumulate in the system, allowing for easy removal.

How do I drain and flush my radiator?

Bury Times: If the sludge has already built up you may need to drain and flush your radiator (Getty)If the sludge has already built up you may need to drain and flush your radiator (Getty) (Image: Getty)

If it's too late and you're already dealing with the heating problem, you may need to bleed and flush your radiator, according to Bishop Plumbing

To do this, you should identify which radiators need to be bled by turning on the central heating and checking each one.

Once this has been done, you should then turn the heating off and allow the radiators to cool.

You will then need to locate the bleed valve which is usually located at the top of the heat source. It is rounded and has a square section for a radiator key or a slit for a screwdriver.

Before opening this and releasing the air and water, you will want to prepare your surroundings using a container and cloth to catch the sludge.

The radiator will then need to be fully removed from its brackets and flushed outdoors. This can be done through the use of a pipe connected to the inlet.

If the sludge is proving tricky to shift, you may want to use a rubber hammer to dislodge it.