A Homeowner’s Guide: change thermostatic radiator valve for DIY heating success

Sometimes, it's obvious when a thermostatic radiator valve (TRV) has given up. You might have a radiator that stays stone-cold even when the heating is on, or the opposite problem – a room that feels like a sauna no matter what you do. Catching these problems early is key to keeping your home comfortable and your heating system efficient.

Other times, the clues are more physical. You might find the valve head is completely stuck and won't turn, or you could spot tell-tale drips and leaks around the fittings.

Knowing When to Change Your Thermostatic Radiator Valve

A dodgy TRV isn't just an annoyance; it’s an energy waster. By failing to regulate the temperature in each room properly, it’s costing you money.

As people across the UK become more energy-conscious, interest in smart heating controls has risen. After a dip in 2020, the market saw a 15.95% recovery in 2021, showing a real shift towards more efficient heating.

A correctly functioning TRV is a small component with a surprisingly big impact. It gives you pinpoint control over the temperature in each room, which can make a noticeable difference to your energy bills and comfort.

Upgrading your TRVs is one of the smartest, most cost-effective ways to get a better handle on your heating. If you're curious about the savings, find out more about how thermostatic radiator valves can slash your heating bills in our detailed guide.

Gathering the Right Tools for the Job

Good preparation is the difference between a frustrating afternoon and a successful repair. Before touching the old valve, make sure you have everything you need laid out and ready to go. The good news is you don't need a massive toolbox for this.

TRV Replacement Tool and Material Checklist

Here's a quick checklist of everything you'll need.

Having these bits to hand means you can focus on getting the job done right, without any interruptions.

Safely Draining and Preparing the Radiator

Before you can fit your new TRV, you need to isolate and drain the radiator. This is a crucial step – skip it, and you'll quickly turn a simple DIY job into a watery mess.

First, switch off your boiler and the central heating system and allow it to cool down completely.

Once it's cool, shut both valves on the radiator. Turn the old TRV clockwise until it stops, usually at the 'off' or '0' setting. Then, tackle the lockshield valve on the other side.

Securing the Lockshield Valve

The lockshield valve helps balance your heating system, so be careful here. As you turn it clockwise to close it, count exactly how many turns it takes. This number is vital for rebalancing the system later. Write this number down somewhere you won't lose it.

With both valves shut, the radiator is isolated. If you want a more in-depth look at this part of the process, our article on how to remove a radiator for decorating has some extra handy tips.

Time to Swap the Valves

With the radiator isolated, you can get started. Place your basin under the old valve to catch any remaining water. Now, grab your two adjustable spanners.

Use one spanner to hold the valve body still – this stops you from putting strain on the pipework. With your other spanner, carefully loosen the large nut connecting the valve to the radiator. Once loose, do the same for the nut connecting the valve to the incoming pipe.

Fitting Your New TRV

Before screwing on the new valve, prepare the threaded 'tail' that goes into the radiator. Take your PTFE tape and wrap it clockwise around the threads about 5-7 times. This creates a watertight seal.

Pro Tip: When tightening, aim for a firm, snug fit. Over-tightening can damage the threads or fittings, leading to a frustrating leak. It needs to be tight, but not forced.

Screw the new valve body into place by hand first, then use your spanners to secure the nuts. Once everything feels solid, you're ready for the final steps.

Time to Refill and Check for Leaks

With the new TRV fitted, you're on the home straight. Now it's time to get water flowing back into the system carefully to avoid any puddles.

First, open the lockshield valve by turning it anticlockwise the exact same number of turns you used to close it. This keeps your system balanced. After that, fully open the new TRV.

Next, you need to repressurise your system. Head to your boiler and use the filling loop to slowly increase the pressure until the gauge is back in the green zone, usually between 1 and 1.5 bar. If you're not sure how, our guide on using your boiler’s filling loop will walk you through it.

Here’s a pro tip for the leak check: wrap a piece of kitchen roll around the new valve joints. It's the best way to spot even the tiniest drip, as water will show up instantly on the dry paper.

Once you’re confident that everything is watertight, the final job is to bleed the radiator. This gets rid of any trapped air, ensuring it heats up properly.

When It's Smarter to Call a Professional

While changing a TRV is a doable DIY task, it’s vital to know when to call an expert.

Don't try to force badly corroded pipework or a valve that’s completely seized, as this can cause serious damage to your plumbing. A persistent leak after you’ve finished is another clear signal that it’s time for professional help. For those who look after multiple properties, professional property management can be a practical solution for complex repairs.

Ultimately, if you don't feel confident at any stage, it's always safer to contact a qualified heating engineer.

For a guaranteed, hassle-free repair, our vetted engineers at Go Assist are ready to help. We’ll make sure the job is done right, leaving your heating system in perfect working order. Book your repair online today.