What To Do If Your Boiler Overflow Pipe Is Leaking Water

  • A leaking overflow pipe is something that shouldn't be neglected.
  • Learn what you should do next with our in-depth guide!
a copper overflow pipe spilling a large amount of water

A boiler’s overflow pipe, or pressure relief valve, is a copper pipe that leads from your boiler to the outside of your home.

If yours is leaking, then at first, it might not seem like an issue. It’s an overflow pipe, after all, isn’t it supposed to let water out? But this leaking might be more serious than you think. Overflow pipes will only let out water if there is an issue with the boiler.

Identifying the overflow pipe

Only combination boilers have overflow pipes, so you shouldn’t be experiencing any leaky pipe issues from your boiler if it isn’t a combination boiler. However, there are other items in the home that use overflow pipes.

Overflow pipes in your home

The following components of your household should have an overflow pipe:

  • Combination boiler
  • Sink
  • Basin
  • Bathtub
  • Copper cylinders
  • Central heating (both the feed and expansion tank)
  • Cold water feeds and expansion tanks

Finding and identifying a boiler overflow pipe

If it is, indeed, your combination boiler overflow pipe that is leaking water, you will find this pipe outside of your home, built into the wall. The pipe is usually made from copper, but plastic and lead have been used in the past.

The pipe should be on the side of your home. The only pipes that should be on the side of your house will be either an air conditioner drain line or the overflow pipe for a boiler. 

Be certain that the pipe you’ve found is your boiler overflow pipe. As we’ve said, it should be made from copper, but in the event that you find a plastic pipe and no other, it’s better to check with a professional that it’s definitely your boiler pipe.

Plastic pipes are usually used for other components of a house and will require a different type of servicing to a boiler pipe. A plastic pipe is more likely to be a condense pipe, which will leak water whenever you turn on your central heating to make your water run hot.

Why your overflow pipe is leaking

If too much pressure builds up in your boiler, the overflow pipe will leak or release water to ease that pressure build up. Alternatively, the pipe may be leaking if the pressure valve is not fitted correctly – this causes water to leak from the overflow pipe.

How to fix a leaking overflow pipe

In the event that your boiler’s overflow pipe is leaking, the best course of action would be to call an engineer. A Gas Safe registered engineer will have the right training and qualifications to repair your boiler.

Alternatively, if you have the training yourself or are well-versed in the nuances of your home boiler, you may be able to fix small issues without calling an engineer out. We should note, if your boiler is insured, do call an engineer and do not attempt to fix the problem by yourself.

In rented properties, the owner may attempt to come out and fix the issue themselves. Be adamant that you want a professional to come and sort out the problem, as your landlord or landlady are likely not trained engineers and shouldn’t be trying to fix boiler leaks.

The owner of your residence will (or should) have the correct insurance or boiler cover, so they could end up paying out more by attempting to fix the boiler than calling out an engineer.

engineer in blue servicing a boiler
An engineer servicing a boiler.

Why fix a leaking overflow pipe

A leaking combination boiler overflow pipe is a sign that something isn’t quite right with your boiler. Whether it’s a fault with the boiler, an ill-fitting pressure valve, or a build-up of pressure, none of these things should be left alone.

Leaks cause wasted water, which you may pay for depending on how you’re charged for your water usage. In the most radical of situations, if your leak is quite prominent, it could also cause damage to the area around the pipe.

Diagnosing a leak

One of the fastest ways to diagnose that there’s an issue with your boiler is to look at the pressure gauge. When a boiler is leaking, or there’s another issue, you’ll find that your pressure gauge will show a level that is either lower than its usual 1.5, or higher. All boilers should be between 1 and 2.

See Also

Alternatively, check for fault codes on your boiler’s display. The meanings of these fault codes will be outlined in your boiler’s manual. They’re difficult to generalise because each manufacturer has their own codes.

Some leaks can be caused when a boiler’s temperature is higher than it can handle. In this case, it’s better to contact an engineer than deal with the boiler yourself. Safety first, after all!

Any corrosion, cracks, or leaks along any of the boiler’s other pipes also indicate issues. Some of these can be more serious than others and could require the purchase of a new boiler.

What to do next

Once you’ve identified your overflow pipe and are certain that it’s leaking, it’s time to take action.

Contain the leak using a container to stop the excess water from damaging its surroundings. If you have any plants near the leak, it would be best to move them out of the way for now.

Check your boiler pressure to ascertain whether the leak is being caused by low or high boiler pressures. Boiler pressure is easy to fix as long as you know which valve controls it or can bleed radiators by yourself. If not, call an engineer.

If you cannot stop the leak, turn off the stop tap and switch off your boiler. Await an engineer for the issue to be fixed. Small, dripping leaks may not require this, but if there’s a lot of water leaking from the overflow pipe, the situation could be more of an emergency.

Only contact a Gas Safe registered engineer to fix boiler issues that you don’t know how to handle. These are trained individuals who will be able to properly advise you on your boiler and overflow pipe problems.

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