Radiator Not Heating Up? Why And How To Fix It

There’s nothing more inconvenient than discovering that a radiator isn’t heating up. Having no access to heat on demand is annoying, no matter the time of year.

A radiator not heating up is frustrating and could have multiple causes. Also, homeowners can fix some of these problems with elbow grease.

Here’s our breakdown of common causes and how to fix them.

Thermostat Issues

A key component of anyone’s home heating system is the thermostat. Its primary role is maintaining the system’s temperature at the desired setting and ensuring it operates as efficiently as possible.

There are three types of thermostats in the UK:

• Manual thermostats, which need users to set them manually
• Programmable thermostats, which allow users to set and schedule temperatures throughout the day
• And smart thermostats, which can be controlled by your phone.

If your thermostat is not working as it is supposed to or is set incorrectly, it will affect your radiators heating capacity.

Common issues to note include:

• Setting the incorrect temperature on the thermostat.
• If the thermostat is battery-operated, it might need new batteries.
• Or the thermostat needs to be reset and recalibrated.

However, if it is unresponsive, your thermostat might need to be replaced by a professional.

Air Trapped in the System (Needs Bleeding)

Air pockets can form inside the radiator, preventing hot water from circulating properly. These air pockets can start to affect the efficiency of your boiler and lead to cold spots at the top of your radiator.

Air can sneak into a closed heating system for several reasons, which include:

• Leaks in your system
• Air getting trapped during the initial installation
• Or general expansion and contraction of the system over time

If an air pocket blocks the radiator, it needs bleeding.

Basic Steps To Bleeding A Radiator

To fix this issue, you must bleed your radiator, a simple task most people can complete.

Bleeding your home’s radiators will mean gathering a few items, such as:

• Radiator key or a flat-head screwdriver
• Towel or cloth to protect your floor from potential spills
• And a small container to catch any water that escapes

There are several steps to take when bleeding your radiator, which include the following:

1. Turn off your heating system.
2. Using the radiator key or flat-head screwdriver, open the bleed valve slightly until you hear hissing of air escaping.
3. Once water starts to flow out of the valve, close it.

After you complete these steps, you should test whether you can remove the air pocket. Our in-depth guide provides more information about bleeding your home’s radiator.

Faulty Or Stuck Radiator Valves And Blockages

A Thermostatic Radiator Valve (TRV) or manual valve can become stuck due to a buildup of debris and sludge. Over time, sludge and rust build up inside the radiator, restricting hot water flow.

You can fix this by first checking whether the valves are working correctly. First, check if the valve is open. If it’s stuck, gently turn it back and forth to loosen it. However, if the valve is faulty, you might need to replace it.

If you discover a pipe blockage, you must flush out the system, removing dirt and debris. In this worst-case scenario, you must call a Gas Safe-registered engineer to perform a power flush.

Boiler Pressure Is Too Low

Your boiler’s pressure ensures it can circulate its heat efficiently. However, if the boiler pressure is too low, it may not send enough hot water to the radiators.

There are many reasons why your boiler could have a low water pressure, which includes:

• Water leaks in the system.
• Mistakes were made when bleeding radiators.
• A faulty pressure relief valve.
• A broken expansion vessel is leading to a pressure drop.
• Or if you’ve recently repressurised your system, as it can take time to stabilise.

Before starting to address the issues, check the boiler’s pressure gauge. When cold or warm, it should read between 1 and 2 bar.

If it is below 1 bar, you must repressurise your boiler.

Basic Steps To Repressurising A Boiler

To begin repressurising a boiler, you will need to follow these steps:

1. Turn Off the Boiler

Switch off the boiler and allow it to cool completely. Usually, a fuse spur (a sizeable square switch) turns the boiler on and off. If not, it is sometimes plugged into a wall socket.

If in doubt, simply switch off the home’s trip switches.

2. Locate the Filling Loop

You will need a filling loop to fill your home’s heating system. A filling loop is a pipe that connects the unit to the council’s main water feed. Usually, a boiler’s filling loop is a silver flexible hose with valves on both ends, usually beneath the boiler.

There are two types of filling loops:

• External Filling Loop: A detachable metal braided hose with two valves. It connects the cold water mains to your central heating system.
• Internal Filling Loop: Integrated into modern boilers, requiring either a key or lever to operate.

If you use an external filling loop, it must be removed when the repressurising process is complete.

3. Open the Valves Slowly

When the filling loops are attached, turn both valves counter clockwise to allow water to flow into the system.

You should hear water moving into the boiler.

4. Monitor the Pressure Gauge

Monitor the pressure gauge as the system fills. Turn off the water supply when the pressure reaches 1–1.5 bar (as your boiler manual recommends).

Once the valves are closed, remove the filling loop if required.

5. Turn the Boiler Back On

Switch the boiler on and check for proper operation. If the pressure drops again quickly, a leak may need professional attention.

We’ve also created an in-depth guide to repressurising your home’s boiler.

Central Heating Pump Issues

You may need a central heating pump to circulate the heated water from your boiler throughout your home’s heating system. However, a faulty or inefficient pump will not effectively circulate hot water.

Common causes for a heating pump experiencing issues are:

• Blockages or sludge build up in the system
• Air trapped in the pump
• Worn-out or faulty pump
• Electrical or wiring issues
• And an incorrect pump speed setting

If you suspect the central heating pump is the problem, check how it is running. If it makes unusual noises or is not working, your home’s central heating pump might need cleaning or replacement.

Radiator Balancing Needed

Balancing a radiator system involves adjusting the flow of hot water to each radiator to ensure even heating throughout your home.

If your home’s system is improperly balanced, some radiators heat up while others don’t.

To fix this issue, you must balance your home’s radiators correctly. Balancing them can be tricky, but most homeowners can accomplish it.

Basic Steps To Balancing A Radiator

If this process is one step beyond your capabilities, always hire a professional to help.

However, if you’re ready, make sure that you have the following items:

• Radiator bleed key or flat-head screwdriver;
• Adjustable spanner or plumber pliers;
• And digital thermometer or infrared thermometer.

Step 1. Turn Off the Heating

As always, safety comes first. Turn off your central heating system and let all radiators cool entirely.

Step 2. Bleed All Radiators

Use a radiator key to release any trapped air, exactly like you would do while bleeding them.

Step 3. Identify the Radiator Closest to the Boiler

Finding the radiator closest to the boiler is the radiator that usually heats up the quickest.

Check all radiators by turning the heating back on and feeling which one gets hot first.

4. Turn Off the Lockshield Valve

The lockshield valve is the small valve on one side of the radiator, usually on the opposite side of the thermostatic or manual control valve. Use a spanner to turn it clockwise until it is fully closed.

5. Fully Open All Radiator Valves

Open the manual or thermostatic valve fully on each radiator and let the radiators heat up thoroughly.

6. Adjust the Lockshield Valve for Each Radiator

Starting with the radiator closest to the boiler, slowly turn the lockshield valve anti-clockwise to open it slightly.

Using a thermometer, measure the temperature difference between the two radiator pipes, which are referred to as the flow (inlet and hot water) and return (outlet and cold water).

The perfect temperature you’re looking for is a 12°C difference between the flow and return pipes.

7. Repeat for All Radiators

After you’re happy, repeat the process to the next radiator. As you move to radiators further from the boiler, you may need to open the valve slightly more.

Once all radiators are balanced, let the system run and check if all radiators heat up evenly.

However, if you’ve read this article and still haven’t found a solution, you should call a professional for help.

Call A WarmZilla Gas Safe Registered Engineer

There’s no need to struggle with repairing a radiator when a qualified engineer can promptly diagnose the issue.

WarmZilla provides nationwide service, with Gas Safe registered engineers available to assist you within 48 hours.