Radiator Not Heating Up: 7 Possible Causes

Winter in Cambridge is cold enough without your radiator not heating up.

When you’ve just wrapped up a windswept walk at Wicken Fen or a spot of Christmas shopping on Green Street, you want to return to a warm, cosy home. Not an uncooperative radiator that leaves your house feeling like the Arctic.

No need to grit your teeth and bear it, though! Let’s get troubleshooting and explore seven common causes for a radiator that’s not heating up.

1.  Air trapped in the radiator

Trapped air is one of the most common causes of a cold radiator. Air bubbles can accumulate in the system over time and prevent hot water from circulating freely. A telltale sign? The bottom of the radiator is warm, but the top remains ice-cold.

You’ll need to “bleed” the radiator to fix this. Don’t worry, it sounds complicated but it’s actually quite simple:

• Locate the bleed valve on the side or top of the radiator. Use a radiator key or a flathead screwdriver to turn it counterclockwise.
• Make sure the radiators are off to avoid hot air and water scalding your hands.
• Have a towel or bowl handy to catch any water.
• You’ll hear a hissing sound as air escapes. Close the valve once water starts dripping out.

Like many household issues, radiators benefit from proactive, as opposed to reactive, care. Regularly bleeding your radiators – especially before winter sets in – can prevent this issue from cropping up.

2.  Blocked valve or thermostatic radiator valve (TRV)

If bleeding doesn’t solve the problem, the next suspect for a radiator not heating up could be the valves. These small but mighty components control the water flow of your system and over time they can get stuck or clogged.

If you have a thermostatic radiator valve (TRV), check if it’s set correctly. Sometimes the valve itself gets a bit stubborn, especially if it hasn’t been adjusted in a while.

Start by gently turning the valve to see if it’s stiff. If it doesn’t budge, give it a bit of a “coax” and see if there’s an underlying blockage. It’s probably best to call a plumber if this quick DIY fix doesn’t work.

3.  Sludge build-up in the radiator

Older radiators, particularly those in hard water areas like Cambridge, can suffer from a build-up of sludge and debris over time. This sludge forms when rust, dirt and scale settle at the bottom of the radiator and stops hot water from circulating properly.

How do you know if sludge is the culprit? Check if your radiator feels warm at the top but cold at the bottom. This is one of the most common signs of poor hot water circulation.

You’ll need to flush your radiator to solve this. Here are your options:

• If you’re handy, you could try flushing the radiator yourself by draining it and flooding water through to clear out the gunk. But be warned – it can be messy work!
• Alternatively, hire a plumber to carry out a professional power flush. This will fully clean out your radiators and pipes to restore heat and improve the overall efficiency of your system.

Really, the best fix for sludge is preventative care. Regular maintenance can help prevent sludge from building up in your radiators and keep your boiler performing at its best.

4.  Unbalanced heating system

Noticed a radiator not heating up? An unbalanced heating system is a common issue in homes with multiple radiators. The problem sees some radiators heat up in record time while others stay stubbornly cold.

Balancing your system involves adjusting the flow of hot water through each radiator to ensure even heating throughout the house. This is something you can try yourself but requires a bit of patience and know-how. If you’re unsure, your best bet is to call in a professional.

5.  Issues with the boiler or pump

Sometimes, the problem isn’t with the radiator at all but with your boiler or pump. Modern boilers typically display an error code if something is amiss, which gives you a clue as to the issue. For serious problems, though, it’s best to call in a professional engineer.

6.  Incorrectly set thermostat

It might seem obvious, but it’s worth double-checking your thermostat settings. Sometimes, thermostats get accidentally adjusted or turned down. Try raising the temperature on the thermostat a few degrees to see if it prompts the radiators to heat up.

A couple of things to keep in mind:

• If you have a “smart” thermostat, make sure it’s connected to your system properly and that any scheduled heating times match your preferences.
• A compatibility issue could be at play if you’ve had recent work done on your heating system or thermostat.

Checking these small details first could save you a call-out.

7.  Radiator size or placement issues

In some cases, your radiator itself simply might not be up to the job. A radiator that’s too small for the room won’t provide enough heat and will leave the space feeling colder than it should. Similarly, radiators in draughty areas (like near a door or a window) will have to work much harder to heat the room.

If your radiator’s working but you find that certain rooms in your home are always cold, it could be worth upgrading to a larger system or repositioning it for maximum efficiency.

When to call in the professionals

If you’ve tried the above steps and you still notice your radiator not heating up, it’s probably time to bring in a professional. A local plumber can quickly diagnose the issue and get your radiator back to its best. Whether it’s a valve replacement, system flush or balancing, Plumbox Cambridge is here to help.

With years of experience in the Cambridge area, we know the ins and outs of heating systems in the East of England and can provide solutions tailored to the unique needs of your home.

No need to suffer in silence. With a bit of troubleshooting, and some hands-on help from the experts, you’ll be warm as toast in no time. Contact us today to book a service with an expert heating engineer or request a no-obligation quote.