How to repair a thermostatic radiator valve (TRV)

How to repair a thermostatic radiator valve (TRV)

If one of your radiators isn't getting hot, then you may have identified that your thermostatic radiator valve isn't working properly.

This is a very common problem with TRVs, particularly at the start of the colder months, after a summer of not needing to use your radiators much. The most likely cause is that the little pin within the valve has got stuck.

Fortunately, this is easy to repair, as we'll explain below.

What is a thermostatic radiator valve pin?

The pin that sits at the top of every TRV is a critical component that needs to be functioning correctly in order for your radiators to get hot.

The heat-sensitive pin dynamically expands and contracts according to temperature fluctuations in the room. If the temperature falls below a certain temperature, the pin will automatically move up to allow more hot water through the valve and into the radiator. If the room temperature hits the desired level, the pin will press back down to stop the water flow.

It's a really good, energy-efficient system that only uses hot water when it's absolutely necessary, keeping your gas bills lower than they might otherwise be. Of course, this is dependent on the thermostatic valve working properly.

What causes a thermostatic radiator valve pin to stick?

The most common reason the pin inside a TRV gets stuck is due to a lack of use. 

During the UK summer in the UK, we have an extended period where we do not really need to use our radiators much. Even during bad summers, we will experience wet weather and complain it's not as warm as we like, but it's rare we need to actually put on our heating.

Because of the naturally elevated temperatures during the warmer months, the pin will recognise no water needs to be allowed into the radiator. The pin will constantly be in the down position for an extended period, pressing against the washer below.

Being in this depressed position for such a long time can cause the pin to become stuck against the washer, stopping the washer from popping back up when the temperature gets colder. As a result, when winter arrives and the central heating comes on, many discover to their dismay that their radiator won't get hot.

This small, but very annoying, issue is very quick to fix and something you can do yourself with just a few basic tools. If you want a greater understanding of TRVs, please read our article How Do Thermostatic Radiator Valves Work?

How to repair a thermostatic radiator valve - step by step guide

Tools you'll need

  •  Adjustable spanner
  • Pair of grips
  • Old towel or sheet (to protect the floor)
  • Water receptacle (just in case)
  • WD40

Steps

  1. Go to the lockshield valve first. This is the valve on the return end of the radiator, the other side from the TRV.
  2. Take a pair of adjustable pliers and turn the valve anticlockwise one full turn. This will open the valve.
  3. Go to the TRV. Open the valve fully, by twisting it to the highest number or setting.
  4. After opening both valves, remove the head of the thermostatic valve by loosing the nut just underneath the head.
  5. Take your grips and gently clasp the exposed pin, carefully moving the pin up and down to free it off. Once free, you should be able to push the pin up and down.
  6. Spray a small amount of WD40 on the pin to keep it loose in future.
  7. Switch on your central heating to see if the radiator gets hot.
  8. If not, then follow our guide on How To Bleed A Radiator to see if this solves the problem.
  9. Check your radiator again. If it still won't heat up then it's time to call a professional.

The video below shows James the professional plumber going through the exact process of fixing a stuck pin inside a thermostatic radiator valve.

Preventative measures

Heating and radiator expert, Nic Auckland, has a good tip for making sure your TRV pin doesn't get stuck next time:

"When the weather starts improving and you get to the stage where your heating is going to be switched, there's a useful little task you can perform first. Open the valves as described in the steps below and then turn off your heating. This will help to ensure the pin doesn't get stuck in the off position and will hopefully mean your heating works perfectly when you switch it on again in the autumn. You'll pleased you've done it!"

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