Why Is Your Home Radiator Not Heating Up? (And How to Fix It)

If your home radiator is not heating up properly, you’re not alone in feeling the chill. This issue, common in hydronic heating systems, can leave you feeling frustrated, especially during the colder months when you rely on it the most. A radiator that’s not heating enough—or not heating evenly—can be caused by a variety of factors, from trapped air and sludge buildup to faulty valves or an unbalanced system.

The good news is that many of these problems can be fixed without calling in a professional. In this guide, we’ll walk you through the most common reasons why your home radiator is not working properly and provide step-by-step solutions to get it working efficiently again. Whether you’re dealing with cold spots, uneven heating, or a completely cold radiator, we’ve got you covered.

Common Causes and Solutions for a Radiator Not Heating Enough

Trapped Air

Trapped air is one of the most frequent reasons for radiators not getting hot or heating properly. Air can enter the system for several reasons, such as prolonged inactivity, a faulty pump, leaks, or even rust and hydrogen buildup inside the pipes. When air accumulates in the heating system, it rises to the top and prevents hot water from filling the entire unit. This results in cold spots, particularly at the top of the radiator, while the bottom may still feel warm.

To fix this issue, you’ll need to bleed the radiator.

Steps to Bleed a Radiator and Remove Trapped Air

1. Turn off the heating device and let the water cool.
2. Locate the bleed valve at the top of the radiator.
3. Place a container and towel below the valve to catch drips.
4. Insert a radiator key or flat screwdriver and turn it counterclockwise until you hear a hissing sound (air escaping).
5. Once the hissing stops and water begins to flow, close the valve by turning it clockwise.
6. Turn the heating back on and check for even heat distribution.

If the water pressure drops after bleeding, top up the radiator.

Thermostat Set Too Low

Another common issue is a thermostat that’s set too low resulting in a cold radiator. The thermostat controls the boiler’s operation, and if it’s set to a temperature that’s too low, the boiler won’t produce enough heat to warm the radiators effectively. This can leave your home feeling chilly, even when the heating is on.

To resolve this, check the thermostat settings and adjust the temperature to a higher level if needed. It’s also a good idea to ensure that the thermostat itself is functioning correctly. Older or faulty thermostats may not accurately regulate the temperature, in which case replacing the thermostat might be necessary.

Closed or Broken Radiator Valve

Radiators have two valves: a thermostatic valve, which controls the temperature, and a lockshield valve, which regulates water flow. If either of these valves is closed or broken, the radiator won’t receive enough hot water to heat up properly.

Start by checking both valves to ensure they’re open. If the valve is stuck or corroded, you can try gently tapping or wiggling the pin inside the thermostatic valve to free it up. However, if the valve is broken or beyond repair, you’ll need to replace it with a new one to restore proper function.

No Water Circulation

Proper water circulation is essential for radiators to heat evenly. If water isn’t flowing through the system as it should, some radiators may stay cold while others heat up. This can happen due to a faulty circulation pump, low water pressure, or air locks in the pipes.

To address this, first check the pump to ensure it’s working correctly. If the pump is faulty, it may need to be repaired or replaced. Next, check the water pressure in the system and top it up if necessary. Finally, bleeding the radiators can help remove air locks that might be blocking water flow.

Blockage Within the System

Over time, sludge, rust, or debris can build up inside the radiator or pipes, causing blockages that disrupt the flow of hot water. This often leads to cold spots, particularly at the bottom of the radiator, and reduces the system’s overall efficiency.

To fix this, you can flush the system using a sludge cleaner and water to remove the buildup. For more severe blockages, a professional power flush might be required. Regular maintenance, such as cleaning the system annually, can help prevent sludge from accumulating and keep your radiators functioning efficiently.

Why Is Only Half of My Radiator Hot?

A radiator that heats unevenly—with one half hot and the other cold—is a common issue. Fortunately, it’s often easy to fix if you have basic knowledge and the right plumbing tools.

Start by identifying where the cold spots are: at the top, middle, or bottom of the radiator.

• Cold at the Top, Warm at the Bottom: This usually means air is trapped in the upper part of the radiator. The solution is to bleed the radiator to remove the trapped air.
• Cold in the Middle or Bottom: This often indicates sludge buildup. Flushing the system with water and a sludge cleaner can resolve the issue.

For more complex problems, especially with open or closed heating systems, it’s best to consult an expert.

Why Are Some Radiators Not Heating Enough? How to Balance a Radiator

If some radiators aren’t as hot as others—like two upstairs elements being warm while one downstairs stays cold—your system may need balancing. Those ones that are closer to the boiler often heat up faster, while those farther away may stay cold if the system isn’t balanced.

Instructions to Balance a Radiator

1. Turn off the heating and let the radiators cool down.
2. Locate the lockshield valve (where cold water exits the radiator) on the radiator closest to the boiler. Close it completely.
3. Turn the heating back on and gradually open the valve by about 25% (¼ turn). This forces hot water to flow to the next radiator.
4. Move to the next radiator and open its lockshield valve by 50%, then the next by 75%. The furthest one from the boiler should have its valve fully open.
5. Adjust the valves until all radiators heat evenly.

For precision, use a thermometer to measure the temperature difference between incoming and outgoing pipes. Aim for a difference of around 50°F (11°C).

Related: Compare steam vs. hot water radiators

How to Improve Radiator Performance

1. Use Reflectors: Radiators often lose heat to outside walls. Install reflectors between the radiator and the wall to direct heat back into the room.
2. Clean Radiators: Regularly flush the system to remove sludge and rust. Clean the exterior to remove dust, which can act as an insulator.
3. Top Up the Radiator: Ensure the system has enough water to function properly.

Proper Maintenance Is Key!

Radiators in North America and Europe typically run for 3-5 months during fall and winter. To ensure reliable performance, maintain your system before the heating season begins. Regular maintenance enhances efficiency, prevents breakdowns, and keeps your home warm and comfortable.

Don’t take your heating elements for granted. A little attention can go a long way in avoiding cold days and high energy bills.