Radiator leaking water from bottom? Three DIY answers to fix

Leaking radiator onto towel on floor
(Image credit: Getty Images)

A radiator leaking water from bottom is not an uncommon problem, but there is often a quick and relatively easy fix for confident DIYers. You might be really lucky and it's simply a tightening of a nut to solve the problem.

While most of us hope for the easiest of fixes it is more likely you will need to do a little more work. The first thing you want to do is identify the leak. Is it coming from the radiator, is it coming from the nut or from the valve itself. Once identified you can get it sorted.

After you’ve fixed your leak and replaced the radiator you will need to know how to bleed a radiator to get it back up to full working order.  

How to stop radiator leaking water from bottom

If your radiator is leaking from the bottom and leaving puddles on the floor it is typically a leaking valve that’s causing the problem. Here’s how to sort it.

1. Tighten the bolt
Radiator valves are attached to a radiator by a nut typically known as a union nut. A simple tightening of the nut may well sort out the issue. This is the first port of call and if you're lucky it will work. If not, it's on to the next solution.

2. Refit valve
The next option is to refit the valve. If the leak is coming from the union nut and the valve it may simply be a matter of adding or replacing PTFE tape around the thread. But before you can do this you will need to know how to isolate a radiator, which is effectively closing the valves on the radiator to stop the water flow and then drain. 

Once isolated, undo the union nut, drain the radiator and dry the thread on the valve when finshed. Now get the PTFE tape and wrap around the thread and do the union nut back up.

3. Replace the valve
If the radiator valve itself is leaking rather than the joint, then remove the old radiator valves and replace with a new one. You will need to check what size pipes you have, these are typically 15mm or 10mm depending on what system you have. Make sure to check out our how to fix a leaky radiator guide for more help with this.  

What do I need to do if it's not the radiator valve? 

If the radiator valve is not the problem then there may be a leak in the radiator itself. If you have an old radiator there may be a rust spot that has finally cracked. These are often found on painted radiators trying to hide rust spots. Look for areas that have bubbled up and place a dry finger on the area and see if it is wet.

Alternatively, note where the water is pooling and look up vertically. If it is the radiator, leaks will be close to the vertical line. Note it might be in the inside or the back of the radiator, making it harder to spot. If the radiator does prove to be leaking, it's time to replace the radiator. 

How much does it cost to replace a radiator? 

If you are replacing a single radiator on a DIY basis the cost will effectively be the cost of the radiator and new valves. Radiator prices vary depending on what type of radiator you are looking to buy. But a common sized (800mm/1000mm) single panel white radiator seen in a lot of homes will cost you around £50-£100. 

TRV valves cost around £10-£30 while basic lockshield valves cost around £5. You can pay more if you want something more than the basics, for instance these Tado smart TRVs costing £199.99 for three on Amazon

If you want to pay a plumber to remove and replace a radiator you should expect to pay around £150-£200 plus the cost of the radiator. If you want the radiator removed altogether expect to pay up to £100 for removal, disposal and capping the pipes.

If you are looking to replace more than a single radiator and do not have much experience working with radiators, you should seriously consider consulting a plumber to see how much they charge. 

Will turning off a radiator stop it leaking? 

Turning off a radiator will stop water flowing through the pipes and into the radiator. This is unlikely to stop any leaks as the water will still be sitting in the radiator and the valves, but it will slow down the leak as no water will be passing through.

However, once you have isolated a radiator you can undo the valves and drain the radiator. Make sure that you have enough containers and towels at the ready to catch the water. An average sized single panel radiator should release around 2-3 litres of water. A double panelled radiator will obviously release more, so be prepared. 

Obviously, an empty radiator means that any leaks from the radiator will stop and if the union nut was the problem then this will stop the leak. However, if the valve is the problem this may carry on leaking. Get a towel and wrap it around the radiator valve to help absorb any leaks.

A leak might be one reason that your radiators are not reaching their maximum temperature. But as with a lot of plumbing problems it's not always that simple. Check out our radiator not heating up quick fix guide for help with any heating and radiator issues.  

Steve Jenkins

Steve is Homebuilding & Renovating's DIY content editor, and has been a writer and editor for two decades. He is an avid DIYer with over 20 years of experience in transforming and renovating homes. He specialises in painting and decorating, but has strong all-round building skills, having previously worked in the industry for 10 years.