How to Fix a Leaking Radiator Like a Pro

A leaking radiator is one of those household headaches that never seems to strike at a good time. If you’ve spotted a suspicious puddle under the bathroom radiator or notice a faint hissing sound ruining your sleep, chances are you have a leaking radiator. Either way, ignoring it isn’t an option. Any negligence may result in a sky-high heating bill or a mouldy patch on your carpet or floor.

The only silver lining is that you don't always need to call a plumber. After dealing with this myself, I can say all you need are a few basic tools and a calm head, and most leaks can be tackled in under an hour. Here is a complete step-by-step guide on how to fix a leaking radiator yourself.

Tools You Need For Radiator Leak Repair

• Adjustable spanner

• Screwdriver (flathead or Phillips, depending on your radiator)

• Old towels or rags

• Radiator sealant 

• A bucket

• PTFE tape 

Here we have discussed how to stop the radiator dripping as DIY. We have discussed complete details about the process.

Step I: Find Where the Leak Is

Not all leaks become obvious. First you need to start by drying the radiator and pipes with a towel. Then, look closely for:

• Drips from valves that are common around the thermostatic valve (the knob you twist to adjust heat). You might also witness some leakage from the lock shield valve (the plain cap on the other side).

• Corrosion on the radiator body in the form of rusty patches or tiny holes near the bottom.

• Pooling water near the joints where pipes meet the radiator.

If water’s spraying out under pressure, turn off your heating immediately and call a pro. 

Step II: Tighten Loose Valves

Most leaks are caused by loose fittings. In this case:

1. Turn off your heating system first because working on a hot radiator can risk burns.

2. Make sure to place a towel under the leaky valve to catch drips.

3. Use an adjustable spanner to gently tighten the valve nut (the hexagonal part connecting the valve to the radiator). 

Wait 10 minutes. If the leak stops, you’re done! If not, move to Step 3.

Step III: Seal Minor Leaks with PTFE Tape

In case there are leaks around the valve threads or pipe joints:

1. Turn off the heating and let the radiator cool.

2. Unscrew the leaking valve/pipe by using a spanner.

3. Wrap PTFE tape clockwise around the thread 5–6 times. This creates a watertight seal.

4. Now reattach the valve and tighten. 

Step IV: Use Radiator Sealant for Small Holes

On the other hand, if you find a pinprick leak in the radiator body, prefer applying sealant for a quick fix. To do this, you must

1. Turn off the heating and bleed the radiator to reduce pressure.

2. Follow the sealant instructions – most require pouring it into the system via a radiator valve.

3. Turn the heating back on. The sealant will circulate and plug small holes.

However, this is a temporary fix. Make sure to replace badly corroded radiators soon.

Step V: Check the Radiator Pressure

Sometimes low system pressure can also cause leaks in the radiator. To adjust this, you first need to locate your boiler’s pressure gauge (it’s usually on the front panel). If it’s below 1 bar, you might have to top up the system using the filling loop (refer to your boiler manual). For reference, the ideal pressure should be 1–1.5 bar. If you notice it exceeding the range, bleed your radiator to release the excess.

Step VI: When To Call a Gas Safe Engineer?

Not all radiator leaks should be DIY repairs. For example, if you notice that the radiator leak stems from corrosion holes in the radiator body ( often appearing as rust spots or weeping metal) or in any case you are unable to identify the cause or are uncertain about the source, it’s time to call a professional. 

Here is what to do if you notice the radiator leak from an unknown source. 

1. Turn off the water supply to the radiator to prevent further leakage and potential damage. 

2. It’s better to drain the entire system before the next step. Locate the drain off valve. It’s usually found on the lowest radiator or near the boiler. Attach a hose to the valve and run it outside or into the bucket (to collect the drained water)

3. Next open the radiator valve. Use a radiator key or plier to turn the valve counterclockwise. Let the water drain completely.

4. You can speed up the water drainage by opening the bleed screw usually found on the upper floor radiator (usually designed to release trapped air).

Once you are done with draining all the water from the radiator, you can call a gas safe registered engineer. You have a legal obligation to only hire a registered engineer for any repair-related boilers and gas systems. This also includes replacing radiators connected to combi boilers. Once an engineer arrives, they will be responsible for the following tasks. 

• Assessing whether the radiator can be repaired or needs a replacement.

• A complete check for system-wide corrosion (common in hard water areas such as London and Birmingham) 

• If required install a new radiator, ensuring it's compatible with your boiler pressure and BTU output.

Why Not DIY Corroded Radiators?

There are many reasons you should avoid corroded radiators leaking problem fix as DIY. The first is that corrosion weakens the metal. If you try to fix the leaking part through welding or patch holes, it can cause the radiator to rupture due to pressure. Secondly, improper radiator leak repair strains the boiler leading to costly breakdown especially if you are fixing the combi system. Additionally, temporary fixes like epoxy putty often fail silently causing mold or structure damage over time. 

How To Prevent Radiator Leaks

There are many ways you can prevent radiator leaks. Here we have discussed a few.

1. Adding inhibitor fluid can prevent the radiator from corrosion and limescale buildup which is common in UK hard water areas. So, I highly recommend using it for your radiator. You can simply use it by turning off the heating and letting it cool down. Then locate the radiator feed pipe or header tank and pour 500ml to the radiator. You will need to use the fluid every 3 years or after draining the system.

2. Radiator bleed can also provide some protection against rusting. It is because trapped air may create cold spots making the boiler work harder and increasing pressure resulting in leaks. So, consider bleeding your radiator every 3 to 6 months or if you hear gurgling sounds. Always check the boiler's pressure gauge and top up the filling loop if it drops below bar 1. 

3. An annual boiler service by a gas gas-safe engineer is highly recommended especially if you live in hard water areas in the UK such as London and Birmingham. It will cost you around £80–£120 annually but saves £1,000+ in emergency repairs. The annual check will involve testing system pressure and checking for leaks. Inspecting radiators for early signs of corrosion. And finally cleaning or replacing sludge-filled magnets in magnetic filters etc.

4.  I recommend not to paint your radiator as it may hide cracks or corrosion allowing for leaks to develop without notice. It can potentially seal the valves shut making future radiator repair in the UK difficult. Instead, you can use a soft cloth to clean the valves and apply a thick layer of WD-40 to prevent rust. 

Ending Thoughts 

There you have it, my own learning experience fixing the leaking bathroom radiator in the UK. Most of the time radiator fixing responds well to this straightforward approach. However, if you have a combi radiator or discover leaking is due to corroded radiators then it's time to call the professional. You have got the knowledge and can now fix most radiator problems.

Frequently Asked Questions