My Boiler Is Leaking Water From The Bottom (Causes & FIX)

If your boiler is leaking water from the bottom you are probably panicking, worrying whether it is safe, and dashing to call a repairman. But before you shell out a fortune to get an engineer to visit, take five minutes to read this short guide.

Our panel of experts have shared their top tips on how to fix a boiler that is leaking from the bottom and they might just save you a big outlay on repairs.

A leaking boiler is many people’s worst nightmare. Most of us don’t know how to fix them and will be scared about whether the issues if dangerous or not.

An emergency callout to a plumber is likely to cost you a tidy sum so before you spend, it is well worth reading through our guide.

Our team of heating engineers and boiler experts have shared their top tips on how to fix a boiler that’s leaking from their bottom. Their advice covers all major brands including Viessmann, Baxi, Vaillant, Worcester Bosch, Glow-Worm, Ideal and others.

While some causes of your leak will require an engineer, others might be dealt with more easily by investing in a new boiler, while there are some that can even be fixed yourself

It is well worth taking five minutes to read this guide. It could end up saving you a big repair bill.

If you’re sick of sinking cash into your rotten old boiler, a replacement is an option. Heatable are an online boiler installation company. They have lower boiler repair costs and have streamlined sales, so they’re able to offer installation prices lower than most. You can get an online fixed price using their boiler calculator.

What kind of fuel does your boiler use?

Grab your fixed price online by 3PM, and get next-day boiler installation.

Worcester boilers installed from as little as £1,965.

Boiler Leaking Water from Bottom: The Fix

A leaky boiler is often the result of a small hole or a worn-out seal. This sort of problem does not affect the functions of the boiler but it can still make a mess and make you worry about how safe it is.

If the problem is a minor hole or a worn-out seal, it is possible to fix the problem yourself with a boiler sealant like Fernox F4. This strong sealant works within 1-24 hours so you can quickly figure out if this is the problem or not.

The tricky bit is finding the source of the leak. This can be difficult to identify and you might find you are unable to do so without the help of a trained engineer. But if you can spot where it is coming from, using a sealant which you can buy from most hardware shops, like Fernox F4, will cost you a few pounds rather than hundreds of pounds.

RELATED READING: Best Combi Boilers on the Market (Reviews)

Boiler Leaking From Bottom: Causes

A leak coming from the bottom of a boiler can be caused by a number of different things. In this section, we will outline the six issues that our panel of experts encounter the most:

#1 – Pressure Release Valve

Your boiler’s pressure release valve is a feature which is designed to release water if your boiler is operating above its usual working range.

The majority of household boilers work at an optimum pressure of 1.3 bar, although they should function fine anywhere between 1 and 2 bar without any problems.

But if you have overfilled your boiler using the filling loop, your boilers pressure release valve will automatically release the excess water to stop it from damaging any of the essential parts inside your boiler.

#2 – Heating Pump Leaks

A lot of boiler issues actually stem from the central heating pump. Leaks are one of the most common problems that are seen.

If the leak is coming from your boilers central heating pump, it is likely to be as a result of a blown seal. The seals on a pump can deteriorate over time and, in older boilers especially, it is common for them to blow.

If your boiler has been operating at extra pressure, this can also sometimes lead to a pump seal blowing.

To find out more about how to solve a blown seal on your central heating pump, take a look at our guide on fixing the most common central heating pump issues.

#3 – Auto-Air Vent

One of the failsafe’s built into your boiler is the auto-air vent. If the operating pressure of your boiler is too high, the excess pressure is transferred automatically to the auto-air vent.

Auto-air vent’s act on a pressurised valve. When this valve identifies an excessively high pressure, it releases some of that pressure. But it is fairly common for this valve to stick, especially if it hasn’t been used a lot, and this can cause not just excess air but also water to come out.

If that has happened with your boiler, you will find that you have water leaking from the top of the boiler but it will then drip down through the boiler casing and out around the pipes at the bottom.

To fix this issue safely, you will need to employ the services of a qualified heating engineer.

#4 – Boiler Connections

In some cases, our experts said they had seen examples of leaks being caused by boiler connections not being done up correctly.

This is not a common problem and is most likely to be encountered with a new boiler that has not been installed correctly.

If you think this could be the problem with your boiler, you can usually fix it yourself. Just dab the connection with some kitchen towel to dry it and then leave it for a short time to see if the water reappears.

If it does, dry things again and then simply tighten the connection with a spanner. If this was the cause of the leak, you shouldn’t see any more water appear.

#5 – Heat Exchanger Corrosion

If you have an older boiler, a leak from the bottom of the unit could indicate that your heat exchanger has become corroded.

This is not uncommon and is, unfortunately, one of the few causes of a leak that is a major issue and is likely to be expensive to fix.

The only way to solve a corroded heat exchanger is to replace it with a new one and this is an expensive part and comes with expensive labour costs too. You will definitely need to employ the services of a gas engineer to do the job.

If your boiler is particularly old and out of warranty, you might want to consider whether it is worth replacing this one part or whether it would make more financial sense to invest in a completely new boiler.

A new heat exchanger is likely to cost you in the region of £500-£600. But if you head to an online boiler installer like Heatable, you can buy a brand-new boiler from a premium manufacturer for around £1,6955.

What kind of fuel does your boiler use?

Grab your fixed price online by 3PM, and get next-day boiler installation.

Worcester boilers installed from as little as £1,965.

The up-front costs are higher, but in the long run, this is likely to save you money and end up being a shrewd investment.

Visit the Heatable website now and fill in their short form (takes only 30 seconds) to get a fixed-price quote and see what a new boiler will cost you today. They can usually guarantee next-day installation on some models too.

#6 – Corroded Pipes & Soldered Joints

A final cause of a leak from the bottom of your boiler might not actually be the boiler itself at all.

Check the pipes and the joints between your pipes and where they connect to your boiler unit. These pipes and joints can corrode over time and end up leaking resulting in a water leak that can appear to come from the boiler.

If you do need to replace pipes of joints, it is best to hire a heating engineer to do the job.

What To Do With A Boiler Leaking Water?

The above six issues are the most common causes of a leak from the bottom of your boiler and hopefully, this guide will go some way to helping you understand what the problem is with your boiler.

As you can see, some of these issues can be fixed yourself quite easily, but others will need the help of a qualified engineer. If you are in any doubt, it is best to err on the side of caution and call out an expert.

They will be able to tell you with confidence what the problem is and recommend the best cause of action.

If you have an old boiler, it is worth discussing with them whether repairing or replacing your boiler is the best course of action. Sometimes, while a repair is cheaper in the short-term, if your old boiler is going to keep developing faults, it can be a false economy.

Why Is My Boiler Leaking From the Bottom: FAQ

We are here to help and we know that a leaking boiler is a cause of panic for most people. So, we also asked our panel of experts what were the most common question they were asked when a customer has a leaking boiler and provided their expert advice in this section:

Is A Leaking Boiler Dangerous?

It is impossible to say for certain whether a leaking boiler is dangerous without identifying the specific cause of the problem, but it can be.

If water is dripping through your boiler, it is quite possible that it is also dripping over electrical parts. Usually, in a boiler, the electrical parts are sealed but it is best not to take the risk. If water does get on your boiler’s printed circuit board or other major parts, it can cause big and expensive problems.

The best advice we can give is to switch off your boiler at once. If you have any doubts at all about the cause of your leak, call out a qualified engineer as soon as possible and don’t switch your boiler back on until they say it is safe for you to do so.

Will A Boiler Leaking Water Mean It Loses Pressure?

If the water leak is coming from your boiler, it is likely to cause the boiler to lose pressure. Any leak anywhere in your heating system will have this effect, regardless of whether it comes from your boiler, your pipes, or your radiators.

This drop in pressure will affect your boiler’s performance and that means you need to try and resolve the leak as soon as possible.

RELATED READING: What size boiler do I need?


If you have a leak coming from the bottom of your boiler, this guide has hopefully helped you get some way towards identifying what the problem is.

As we have explained, there are a few issues you might be able to resolve yourself, but if you are in any doubt, it is best to switch things off and consult with a qualified engineer.

Some problems can be fixed relatively easily, but others will require a more expensive fix and if your boiler is old and out of warranty, you might decide it makes more sense to buy a brand new boiler through a cost-effective online installation site like Heatable.

Have you had a problem with water leaking from your boiler? What did you do to fix it? Do you have any tips we haven’t mentioned in this guide? It is always helpful to hear customers experiences and advice, so please do share them with us in the comment box below.

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