Worcester Boiler Leaking Water

Why is My Worcester Boiler Leaking Water? The Top Reasons

Last updated on June 8th, 2024

A boiler leaking water can cause your boiler to not fire up, rust or become dangerous.

I have been fitting and fixing boilers full-time for over a decade and have repaired many leaking Worcester boilers.

In this post, I’ll share some of what I have learned over the years from my on-the-job leak repair experiences.

Leaking Water From Underneath

There are many places a Worcester Bosch boiler can leak water from, but it’s almost always leaking from underneath.

Water leaking from underneath doesn’t mean the leak is at the bottom of the boiler. The leak could be at the top of the boiler but collects in the bottom of the boiler before dripping out underneath.

The best way to find out where a leak is coming from is to keep checking as high as possible to look for signs of water. Where it’s coming out of the boiler is usually not where it’s leaking from.

Common Worcester Boiler Leaks

Certain Worcester boilers have certain recurring problems which typically get fixed by the manufacturer when they bring a new version of a boiler out or update a faulty part.

Here are some common recurring Worcester-specific boiler leaks I come across:

  • Flow turbine adaptor
  • Flow unit left-hand block
  • Right-hand block

Flow Turbine Adaptor

Worcester boiler flow turbine adaptor leaking
Flow turbine adaptor leaking

A Worcester Bosch combi boiler leaking water on the right-hand side is usually a sign that the plastic flow turbine adapter on the hot water is damaged and needs to be replaced.

This is a cheap part, which I always have on the van, but it can be awkward to replace.

Although the flow turbine adapter is on the right-hand side, the water could be running along the pipes and leaking out of the boiler on the left-hand side.

Flow Unit Left-Hand Block

The flow unit left-hand block is a black plastic unit that gets pinhole leaks in it. This means it needs to be replaced ASAP.

This water is hard to see spraying out but it will create a large drip from the bottom of your boiler.

Boiler Pipe Leaking

When you have a boiler pipe leaking water you will need to do one of these things:

  • Tighten the nut if it’s on a compression fitting
  • Resolder the fitting
  • Replace the section of pipe
  • Solder a patch fitting on

Water Leaking From Overflow Pipe

A boiler leaking water outside means the pressure relief valve is leaking out of the blow-off (overflow) pipe.

The pressure relief valve leaking is usually a sign of other problems causing it to leak, but it often means you will need to replace the pressure relief valve.

You need to find and fix any other problems before replacing it or the new one will just leak again.

Condensate Pipe Leaking

A condensate pipe leaking out of the end outside is normal but if it’s leaking from a fitting inside the house then this could potentially be dangerous.

A frozen boiler condensate pipe can cause it to leak sometimes but condensate water is acidic and eats away at copper and brass which is why they have to be plastic.

If you have a boiler condensate pipe leaking onto a copper pipe, especially gas, then this should be fixed as soon as possible.

Filling Loop Leaking

A boiler filling loop leaking usually means it needs to be replaced.

You can tighten the nuts up if it’s leaking from them but you will probably need to replace the boiler filling loop or filling loop valve.

Flue Leaking Water

A boiler flue leaking water is typically a sign it’s not fitted correctly.

A condensing boiler creates condensate wastewater which is created from the flue gases.

This wastewater needs to run back into the boiler condensate trap via the flue which is why the flue needs to be pointing slightly up and away from the boiler.

If the flue is pointing slightly down (or even straight), the condensate will drip out of the end of the boiler.

If the boiler flue is leaking from anywhere else, e.g. a flue connection, this will need to be looked at and fixed by a gas engineer as soon as possible.

Boiler Leaking Gas

If you can smell gas coming from your boiler then you will probably have a boiler gas leak which needs to be fixed ASAP!

You should turn off the gas at the gas meter if you can, and call your local Gas Safe registered engineer to book an appointment or call the National Gas Emergency Service on 0800 111 999.

Worcester Boiler Problems

Here are some other common Worcester boiler problems you can learn about:


An old Worcester boiler leaking water may be a sign the boiler is on its way out and needs to be replaced soon.

A boiler leaking brown water typically means you have a dirty heating system which is causing problems and a good sign you need to flush the heating system after fixing the leak.

If you have a boiler leaking from any type of compression connection. e.g. a leaking boiler valve on the flow or return, or a boiler drain valve, you should try tightening the nuts with an adjustable spanner.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you found it helpful.


If I turn my Worcester boiler off will it stop leaking?

No, your Worcester boiler will most likely not stop leaking if you turn it off. If it’s leaking condensate water, then it will eventually stop leaking as the boiler will not be producing any condensate.

You should turn the water supply off to your boiler if it’s leaking, as this will stop the leak if it’s on the hot water parts on the boiler.

Is a leaking Worcester boiler an emergency?

A leaking Worcester boiler can be an emergency but most of the time it’s not.

Depending on exactly where the leak on the boiler is coming from, a leaking boiler can sometimes cause the boiler to not fire up when the pressure drops which could be seen as an emergency in the winter.

If the condensate pipe is dripping onto a gas pipe, the acidic condensate wastewater will eat away at the copper and brass and cause a dangerous gas leak emergency.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

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3 thoughts on “Why is My Worcester Boiler Leaking Water? The Top Reasons”

  1. Ruth McCluskey

    Steven, thank you very much for your advice. ( I wish the installer had told us that these leaks are well known to fitters when they recommended the particular boiler to us – we might have chosen differently . )
    We have no hot water now anyway even though the boiler is on as the pressure won’t hold for even a short while and is too low to allow the boiler to function . I will call Worcester in the morning to talk me through anything I need to do to turn it off . I have had 2 nights where I have had to set an alarm to get up and empty the washing up bowl full to the brim of water underneath every couple of hours. I can’t do that fo another 3 nights as it’s doing me no good at all!
    I appreciate your advice , though, so thank you again .

  2. Ruth McCluskey

    Hi, Steven. Our Worcester combi boiler and whole heating system is less than a year old and was obviously a big cost to us. The boiler is now leaking badly from underneath and I called out the company who installed it. They tried to fix it ( a washer had corroded certainly) but said call out manufacturer ( it has a warranty) if still leaking and problem not solved. It continued to leak so manufacturer engineer came out and said it needs new parts . They are coming Monday with parts so meantime I have to keep topping up pressure particularly for heat in the night ( we are elderly) and empty a large bowl every few hours. The engineer was pleasant and helpful himself and was concerned that turning the boiler off totally would leave us without heat at all .
    I feel concerned that a new boiler is already leaking badly – does this happen often and what should I expect to happen ? Is the situation safe for a few days and can the continuous leaking water cause long term damage even over the short period of time.
    Thank you in advance.

    1. Steven Reid

      Hi Ruth,
      New boilers do have problems sometimes whether it’s a leak or a broken part, that’s why they have warranties. Sounds like you’ve just been unlucky with that boiler.

      Not much you can do apart from keep emptying the water from the bowl, or turn off and isolate the boiler which means no heating or hot water. A leak shouldn’t cause any long term damage.

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