A common problem that people have with their central heating systems is a radiator that won't get hot.

One of the first things to do in this situation is to bleed the radiator in case air has got trapped in the system and is preventing hot water from completely filling the radiator.

Bleeding the air out is very easy to do and more often than not, completely solves the problem.

But not always. What if you've bled your radiator and it's still cold after bleeding?



Check your thermostatic radiator valve

A common problem that might stop your radiator from getting hot, even after bleeding, is due to a stuck pin on your thermostatic radiator valve (TRV).

You can check if this is the issue yourself by removing the cap/head on your TRV. (The TRV is the chunkier of your two radiator valves with the temperature control numbers on.)

Underneath the cap, you should see the exposed TRV pin. These can often get stuck in the shut position meaning that water is not able to flow into your radiator.

To loosen the stuck pin, grab a adjustable spanner or set of grips and gently use it to grasp the pin and move it up and down. This should loosen and slacken off the pin, freeing it up and allowing it to allow hot water back into the radiator.

Switch on your central heating system and see if it now starts to get hot.


Flush out your radiator in case of an air lock

If your radiator is still not getting hot after loosening the pin on your TRV, then you could try flushing out your radiator in case there is an air lock in the system.

If you have some plumbing experience, this is something you could tackle yourself, though you may wish to bring in a professional plumber:

  • Shut the TRV and the lockshield valve
  • Get a small towel and put it under the air bleed and open it up with a radiator key
  • That will help to dissipate the pressure in the radiator
  • Remove the whole air bleed assembly
  • Add a 1/2 inch male connection that will allow you to connect to a garden hose
  • Now turn your heating system off
  • Connect the hose so that it goes ideally outside or into a large container
  • Open up the thermostatic radiator valve
  • A large body of water will then flow out of the top of the radiator and out through the hosepipe
  • This will hopefully remove any airlock and allow your radiator to get hot again once you switch your heating back on


Do you need to balance your heating system?

If you've done all of the above and your radiator is still cold, it may be the case that the flow of water around your system is not even, in which case you need to balance your heating system.

A balanced heating system means that the flow of water from the boiler and the pump goes into each radiator in your house evenly.

The radiator that is at the far end of your heating system (furthest away from the boiler) is often the radiator that won't get hot if your system is unbalanced.

To fix this problem and get your radiator hot again, you can follow the step-by-step guide from Jimmy the professional plumber in our video below.



Replace your thermostatic radiator valve

Another explanation for a radiator that is cold even though the heating system is switched on is the possibility that your thermostatic radiator valve needs to be replaced.

We discussed earlier in the article that TRV pins sometimes get stuck into the shut position and can often be sorted out with a quick wiggle of pin in order to free it up.

However, thermostatic radiator valves can degrade over time, especially if they have had a lot of use. The pin in the valve may have corroded, worn away or is simply too stiff for you to free up.

In this case, it's probably a good idea to replace the radiator valve. Not only will this likely solve the problem of a cold radiator, but a new set of valves can give a new lease of life to radiators and add a smarter and fresher look to your room.

In the videos below you can view an easy to follow guide on how to replace your TRV safely and effectively, as well as find out exactly how TRVs work and how they can save you money on your heating bills!




Heating system maintenance

If all these suggestions still haven't solved the issue of your cold radiator, then it's time to call in a Gas Safe Registered Plumber to check over your system and see if there is a more serious underlying problem.

Getting in a professional once a year to inspect your boiler, pump and other parts of your system is a good habit to get into as it can save you from having a costly breakdown when you most need it.

A lot of boiler warranties and insurance terms and conditions actually insist on customers' having maintenance carried out on their systems, so it's worth doing so that you don't invalidate your warranty or fail to get an insurance payout should the worst happen.

Don't forget chemical inhibitor

If you do get a professional to come and look at your heating system, then they should check the inhibitor levels in your heating system as a matter of course.

However, if you are doing a lot of the work yourself, then chemical inhibitor can be a very important factor that is easy to overlook.

Over time, the water that flows through your heating system can react with the metallic internal components. This causes corrosion where bits of metal can flake off into your pipes and radiators, narrowing the flow of the water and causing a sludge to appear in the bottom of your rads.

This makes your boiler and pump work harder and harder to push the water around the system and, if left unchecked, can cause your boiler to breakdown completely.

Adding a chemical inhibitor to your system helps to prevent this corrosion from occurring, giving you a healthy heating system for years to come.

To see an interesting comparison between a system with and without chemical inhibitor, please view the video below.



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