One Radiator Not Heating Up? Causes & Fixes

Contents:

• Key Takeaways
• Quick Checks
• Why One Radiator Is Not Heating Up
• How To Fix One Radiator That’s Not Heating Up
• When To Call A Professional
• FAQs

If you’re having issues with one radiator not working, but the others work normally, it means the fault is a localised one rather than a problem with the entire heating system. If all radiators are not heating up, you are dealing with a system-wide issue instead.

It is common for just one radiator to stop working, even when the rest are fine, and can be attributed to a number of factors. Trapped air, a buildup of sludge and debris, and stuck valves are common causes.

There are many reasons why one radiator may stop working, and each issue has its own solution and means of identifying. Here are a few key things you should know:

 

• Simple Checks – One way to identify what is causing your faulty radiator is to feel for cold spots. Cooler spots at the top of the radiator signal trapped air restricting water flow, while cold spots at the bottom are a sign of a buildup of debris. If the radiator is cold all over, this points to an issue with the valves.

• Solutions – Trapped air blocking water flow can be fixed by bleeding the radiator. Blockages of settled debris can be removed by flushing the radiator, or contacting a professional if the issue is system-wide. Stuck valves can be unstuck by gently raising a central pin in the valve.

• Top Tip – If you suspect there is debris buildup in multiple radiators, or that the fault lies with your boiler system or pipework, it’s always best to consult a professional.

To determine why one radiator isn’t working, there are a few checks you can do:

 

• Inspect Valves – Stuck valves can leave the radiator unable to switch on and prevent hot water from flowing into the panel. Check your radiator valves are open.

• Find Cold Spots – Feel the radiator for any cold spots. If the radiator is warm but has cold spots at the top, this is a sign of trapped air being the issue. If it is warm with cold spots at the bottom, it indicates a blockage instead.

• Check Other Radiators – If other radiators are working fine, this rules out system-wide issues that may relate to boiler pressure and trapped air in the heating system itself.

• Bleeding Status – Radiators that have not been bled for some time may be more prone to holding trapped air

If it is just one radiator that isn’t heating up properly, then the issue is an isolated one. This means the heating system and boiler are working correctly, and the issue lies in the specific radiator itself.

 

The most common issues behind a single radiator not working are:

• Trapped Air – This is when pockets of air form from natural water movement and sit near the top of the radiator, preventing hot water flow and heat transfer to the top. It is indicated by cold spots at the top of a radiator.

• Sludge Blockages – This is a problem, especially for older radiators, and comes about as limescale, rust, and debris within the radiator settle at the bottom, creating a barrier that limits heat from transferring into the radiator. Cold spots on the bottom of a radiator are signs of this.

• Stuck Valves – If the valves on the radiator are stuck, which may be due to extended periods of no use, i.e., the summer months, then they may be preventing the radiator from allowing hot water into it.

 

Radiator cold at the top

 

If you feel cold spots at the top, it means trapped air is the reason why just one radiator isn’t working. This is the result of air rising and forming pockets at the top that block hot water circulation. 

 

To resolve this, you must bleed your radiator. To do this, turn off your heating and let the radiator fully cool down. Then, locate the valve on one side of the radiator at the top, and use a screwdriver or radiator key to slowly turn the valve. You’ll hear hissing sounds as the trapped air escapes. 

 

Once water begins to flow out of the valve, screw it back up tightly before turning the heating system back on.

 

Radiator cold at the bottom

 

Another reason why one radiator may not be heating up is due to a buildup of sludge. This is indicated by cold spots at the bottom of the panel, where the debris has settled and is providing a barrier to the heat transfer.

 

To fix this, you may need to flush your radiator:

• First, turn off the heating and allow the radiator to cool down, ensuring the TRV valve is closed. 

• Place a bucket under the valve and open the bleed valve. 

• Then, take the radiator outside and put a hosepipe in one side to force out the sludge and debris. 

• Keep washing it until the water coming out the other side runs clear. 

• Dry the radiator off, reattach it to the wall, and tighten the valves. 

• Reopen the valves, check for leaks, and bleed the radiator to remove any air that may have entered.

 

For system-wide blockages, the best solution is to consult a professional. If the blockages seem severe, you may also want to consider replacing the radiator, especially if it is old and likely to shed more debris.

 

Radiator completely cold

If the radiator not working in your room is completely cold, this points away from trapped air and blockages. Instead, it would indicate that a seized pin within the valve may be the issue. This is a common cause of a faulty radiator, especially when the radiator hasn’t been used for a long time. 

 

To fix it, unscrew the metal or plastic ring that sits at the base of the thermostatic radiator valve, or TRV’s, head. Once the head is off, you’ll see a small metal pin sticking out of the valve’s body. If it is stuck down, it is blocking the water flow.

 

To unstick it, simply use pliers to gently pull the pin up. Don’t pull so hard that it breaks or flies out, as this can cause a leak – it should pop up automatically with a little bit of force. Use some lubricant on the pin if it won’t come up easily.

 

Once you’re done, reassemble the TRV, and the radiator should now work.

If you have just one radiator in one room that isn’t working, the issue is, thankfully, not a system-wide one and is likely easily fixable.

 

1. Check the Radiator Valves – The first step is to identify the reason why just one radiator in a room isn’t working, and this involves checking the valves are fully open and feeling for any cold spots on the panel. If the radiator is cold at the top, see Step 2. If it’s cold at the bottom, see Step 3. If it’s cold all over, see Step 4.

2. Bleed the Radiator – Cold spots at the top indicate trapped air, which can only be solved by bleeding the radiator to release it.

3. Flush the Radiator – If the issue is a blockage, then the best way to resolve it is to detach the radiator and flush it with water to remove the debris.

4. Check the TRV – Assess whether the thermostatic radiator valve is stuck. If the pin is seized, free it gently using pliers.

If your radiator is still cold after being bled and after valve checks, or you suspect a sludge buildup across multiple radiators, then you should consult a professional. You should also contact a professional if there are issues with the pipework or if boiler pressure issues persist.

 

Though some issues with a radiator not working can be easily resolved, others require professional expertise and attention.