What Can I Do If My Radiator Is Cold At The Top

A properly working radiator should be hot to the touch all over. If it is colder at the top than the bottom, there might be a problem. Luckily, it’s easy to fix. So what can you do if your radiator is cold at the top…

My Radiator is Cold at the Top

The usual reason for the top of a radiator being cold is trapped air. Fortunately, trapped air is common, and there’s an easy fix. At the top of the radiator is a bleed valve. Most bleed valves require a radiator key, but you sometimes find one that can be opened with a screwdriver or spanner.

Bleeding a Radiator

Make sure the heating is turned off and left to cool for half an hour, as the water inside a radiator can be scalding hot. Put some towels down on the floor beneath the valve, and place a container on in, underneath the valve. If there is wallpaper behind the radiator, consider protecting it too.

With the radiator key, turn the valve gently clockwise until you hear hissing. This is air being released. If the cold went halfway down the radiator, you can open it up a bit more to speed the process, but be sure it doesn’t completely come out.

Now, wait as water replaces the air in the radiator. Be prepared to close the valve when you see water coming out.

Now close the valve gently. It is not under a lot of pressure, so it doesn’t need to be too tight: over-tightening can cause the bolt to the thread, which is a bigger problem.

Preventing cold radiator tops

Because the central heating system is under pressure, it’s nearly impossible for air to get in from outside. The most likely cause of air ingress is corrosion within pipes or radiators. The solution is for a Gas Safe engineer to add a retardant to the system to slow down or eliminate corrosion.

It’s also possible for air to enter the system while it’s being filled. Changing the temperature and pressures can let air trapped in water into the system. Bleeding the radiators removes it.

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