A small puddle under the boiler is easy to ignore, especially if the heating still seems to work. But water and boilers don’t mix well, and a leak usually gets worse rather than better. The most common causes are a pressure relief valve letting water out, a loose or corroded joint, a failing pump seal, or a leaking heat exchanger. Some leaks are simple fixes, others mean it’s time to think about the boiler’s future. If you’ve spotted water, our boiler repair engineers cover homes across South London and Kent.
What to do straight away
- Turn the boiler off.
- If water is near electrics or dripping onto sockets, switch off the power to the boiler at the fused spur or consumer unit, if it’s safe to reach.
- Catch the water with a bowl and towels, and move anything valuable.
- Check the pressure gauge and note the reading.
- Call an engineer.
Don’t take the casing off to find the leak. Inside the boiler are gas, electrical and flue parts that only a Gas Safe registered engineer should work on.
Common reasons a boiler leaks water
Pressure relief valve
If system pressure gets too high, the pressure relief valve opens to let water out, usually through a copper pipe that runs outside. A drip from that pipe, or high pressure on the gauge, points to this. It often happens after the system’s been over-filled, or when the expansion vessel has lost its charge.
Loose or corroded joints
Joints and fittings under the boiler can work loose as pipes expand and contract, or corrode over time. These are often the easiest leaks to fix.
Pump seal
A worn pump seal can drip, usually from the bottom of the boiler. On older systems the pump may be outside the boiler near the cylinder.
Heat exchanger
Corrosion can eventually cause the heat exchanger to leak. This is one of the more expensive repairs, and on an older boiler it’s often a sign replacement is the better option.
Condensate pipe or trap
Water around the condensate pipe can come from a blocked or split pipe, or a problem with the trap inside the boiler.
Is a boiler leak dangerous?
A water leak isn’t the same as a gas leak, but it can still be a risk. Water can damage electrical parts inside the boiler, cause corrosion and lead to the boiler losing pressure and breaking down. It can also damage ceilings, floors and kitchen units.
If you smell gas at any time, leave the boiler off, open windows, turn off the gas at the meter if it’s safe, and call the National Gas Emergency Service on 0800 111 999.
Leaking boiler and losing pressure
A leak and pressure loss often go together. If you’re topping up pressure regularly but can’t see any water, the leak may be hidden in pipework under floors or behind walls. Our leak detection service uses thermal imaging and small cameras to find leaks without lifting floors unnecessarily. There’s also more on this in our guide to why a boiler loses pressure.
Repair or replace?
If your boiler is fairly new and the leak is from a joint, valve or pump, a repair is usually straightforward. If it’s 12 to 15 years old or more and the heat exchanger is leaking, a repair may cost a large share of the price of a new boiler. We’ll give you an honest view either way.
Boiler leaks in South London and Kent
Hard water across much of Kent and South East London builds up scale inside boilers and heating pipework. Over time, that adds strain on valves and seals. Older homes in Sidcup, Bexley and Bromley also often have a mix of original and newer pipework, with plenty of joints where small leaks can start.
Frequently asked questions
Can I still use my boiler if it’s leaking?
It’s best not to. Turn it off and get it checked. Running a leaking boiler can damage electrical parts and surrounding areas, and the boiler may lose pressure and lock out anyway.
Why is my boiler leaking from the bottom?
Common causes include a loose or corroded joint, a worn pump seal or a valve letting by. In some cases it’s the heat exchanger. An engineer will need to remove the casing safely to find the exact source.
Why is water dripping from the pipe outside?
That copper pipe is usually the pressure relief valve discharge. A drip means the valve is letting water out, often because the pressure is too high or the valve itself is faulty. Both need checking by an engineer.
Will my boiler warranty cover a leak?
It may, if the leak comes from a faulty part and the boiler has been serviced every year as the manufacturer requires. Check your warranty documents or ask us when you call.
Spotted a leak?
Don’t leave it to get worse. Give us a call on 020 3722 5095 or drop us a message and we’ll come out, find where it’s coming from and get it fixed.