Why my Home Radiator is Not Heating Enough?
Radiator Repair Tips

Home radiators

A step-by-step guide on how to repair a home radiator not heating enough and evenly.

Find out why it takes some radiators to heat up longer or why only half a radiator is hot while the rest is cold.

Use this guide to get answers to the most common radiator problems.

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Common radiator problems

If you find one or more radiators feel cold or not heating up properly, the following issues might be happening:

  • Trapped air
  • Thermostat is set too low
  • Radiator valve is closed/broken
  • No water circulation
  • Blockage within the system

Why only half of my radiator is hot, and the other half is cold?

A radiator not heating up evenly, so half of the radiator is hot, and the other is cold, is one of the most common problems and is often easy to repair. You can fix it yourself if you have basic knowledge about heating and radiators, and the right tools.

The first thing you should do is identify the location of the cold spots, whether it is at the bottom, in the middle, or at the top.

If your home radiator is cold at the top and warm at the bottom, that means air is trapped in the upper part of the radiator. The solution for this problem is to purge air from the system. This is also known as bleeding the radiator.

Find more info on how to bleed the radiator and remove trapped air, below.

The most common reason for the cold areas in the middle of the radiator and bottom is the sludge buildup.

With some basic knowledge and tools, you can easily flush the system out by yourself using just the water and sludge cleaner.

In other more complicated cases, you might want to contact an expert. The complexity of the problem is related to whether you have an open or closed heating system.

Why some of my radiators are not getting hot enough? How to balance a radiator.

If you find some radiators not as hot as others, like two upstairs are hot, and one downstairs is cold, your radiators would need balancing. Some radiators get warmer than others because the heating system is out of balance. Also, as the distance between the boiler and radiators varies and if the system is not correctly balanced, you can expect to see different temperatures from one radiator to another.

Simply said, balancing radiators means adjusting the water flow through the radiators, so they heat up at the same speed and evenly.

To balance a radiator, you would need first to turn off the heating and wait for a radiator to cool down.

Locate the nearest radiator to the boiler and close its lockshield valve (where the cold water exits the radiator), located at the bottom.

Turn the heat back on and gradually turn the valve clockwise - approximately 25% or ¼ of a turn. This way, you will force hot water to find its way to the next radiator so that heated water can get distributed evenly throughout the house.

Then go to the next one and open the lockshield valve about 50%, then the next one around 75%.

The point is to have the valve open the most on the furthest radiator from the boiler.

So, to properly balance radiators, you need to adjust these lockshield valves from the radiator to the radiator until the temperature is evenly distributed, providing maximum comfort and efficiency.

You can even buy a thermometer and measure the temperature of the incoming and outgoing radiator pipes. Then adjust the lockshield valve to get the temperature difference around 50 F (11 C).

How to repair a cold radiator

If a radiator equipped with a thermostatic valve is cold, check that the valve is adjusted correctly (setting 5 is the highest).

It might also be seized up, preventing a radiator from getting hot. The reasons can be internal corrosion and scale buildup.

One of the solutions is to remove the valve cap, wiggle, and gently tap on the metal pin underneath.

Another solution is to replace the valve if it is unrepairable.

How to bleed a radiator and remove trapped air

As mentioned, if the radiator is cold at the top and warm at the bottom, the usual culprit is the trapped air. The most common reasons for the air present inside the system are:

  • No activity for several months (no water movement)
  • Faulty pump
  • Pump installed above the water tank
  • Rust and accumulation of hydrogen
  • Leaks
  • Low pressure

Bleeding the air is a simple procedure that requires only a flat screwdriver or a radiator bleed key, container, and towel.

Tip: Make sure that the boiler and circulation pump are off. Also, let the water cool off.

Locate the bleed valve. The bleed valve is found at the top of the radiator, either on the left or right-hand side.

Make sure a water container is positioned below to collect drips. You can also use a towel to collect any excess water.

Insert a key or a screwdriver into the valve and turn it counter-clockwise until halfway open. You should hear the hissing sound. This is air escaping from the radiator, and once it stops, water will start flowing through the valve.

Close the valve by turning the key or a screwdriver clockwise until the water flow stops.

With the air removed from the system, turn the heating back on and check the heat distribution on the radiator. There shouldn't be any cold spots now.

If the water pressure drops due to bleeding, top the radiator up.

Note: Bleeding needs to be done repeatedly because air enters the system all the time. Ensure to bleed the radiators entirely until you get steady water discharging for a few seconds.

How to improve radiator performance

Use reflectors. As the radiators are installed mainly on the wall and below the window, there could be a lot of heat energy wasted on heating the supporting wall. And if not properly insulated, that heat could be lost.

The solution for this problem is to install reflectors between the radiators and the outside wall so they can direct heat back into your house.

Clean radiators. Clean and flush the radiators regularly or when you find cold spots and unevenly heated radiators. Cold spots at the bottom of the radiator often mean some sludge accumulations. The first indication of the sludge and rust development inside the radiator is black water coming out of the bleeding valve when removing the trapped air.

It is recommended to turn the system off, have water cool down, and remove both lockshield and thermostatic valves. Take the radiator outside and run the clean water through the unit until all the rust, grime, limescale, and dirt are removed. You might want to use special additives to help clean the system efficiently and thoroughly.

Also, clean the radiator from the outside as there might be a thick layer of dust (especially at the back) that acts as an insulator, preventing regular heat exchange with the surrounding air.

Top up the radiator. When water is distributed thoroughly and evenly, the radiator will function properly, and the whole surface will be hot/warm. There will be no trapped air.

Proper maintenance is the key!

The majority of homes in North America and Europe are likely to be operating for most of the fall and winter months, which is approximately 3-5 months. As the radiators will be running almost every day for many months of doing nothing, make sure to maintain the system before the heating season properly. This will not only enhance the radiator's performance but provide reliable operation for a long time without calling for help.

Don't take radiators for granted. Pay them attention, and they will keep you warm and comfortable for a long time without breaking.

If you have any doubts, questions, or need a repair, contact your local HVAC expert to avoid cold days and high energy bills.

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