Why Worcester Bosch boilers like to leak

Common places Worcester Bosch boilers like to leak from

Many modern boilers will leak at some point in their lifetime, but modern Worcester Bosch combination boilers have gained a reputation for leaking.

This post explains where they like to leak from and why they tend to leak.

If you have a Worcester Bosch combination boiler combination boiler installed there is a good chance it may leak at some point depending on when it was manufactured.

In our experience the most affected Worcester Bosch boiler models are the Junior, Si and CDI combination boilers, manufactured between 2005 and 2015.

The issue we talk about in this post doesn’t apply to system or heat-only boilers, obviously they can and do leak but for different reasons.

Where Worcester Bosch boilers leak from

The Junior, Si and CDI boiler models tend to leak from one of three places, sometimes from all three places if you’re unlucky.

If your boiler is leaking from the left hand side it more than likely is the left hand manifold or “flow unit” which has failed.

If the flow unit has failed it won’t cause the boiler to lose pressure, it will just leak constantly until the mains water supply is turned off.

If the boiler is leaking from the right hand side it could be the right hand manifold called the “return manifold”, or a small adapter that sits inside the return manifold called a “flow restrictor adaptor”.

If the return manifold has failed the boiler will generally leak from the right back side of the boiler.

If the flow restrictor adaptor has failed it will more than likely leak from the front right side of the boiler.

Like the flow unit on the left, if the boiler is leaking from either the return manifold or flow restart adaptor,

this will also result in a steady leak that won’t cause the pressure on the boiler to drop, and won’t stop until the mains water supply is turned off.

Cost of repair for leaking Worcester Bosch boiler

The cost to repair your boiler is obviously going to vary depending on who you get to repair your boiler, and which part has failed.

The cheapest, easiest component to replace is the flow restrictor adaptor which sit inside the return manifold.

The flow restrictor adaptor costs less than £10 retail at the time of writing this post.

Slightly more expensive and more time consuming to replace than the adaptor, is the flow unit manifold on the left hand side of the boiler.

The flow unit currently retails for around £30.

The most expensive, time consuming part to replace by quite a big margin is the return unit, which is on the right side of the boiler.

The return manifold currently retails for around £170.

Obviously the cost of these parts doesn’t include the cost of labour which is going to be determined by whoever you get to repair your boiler and how long it takes.

In our experience most of the Worcester Bosch boilers we repair that are over 5 years old, that haven’t been serviced by us within the last 12 months require additional work.

This is why we service and repair every boiler we fix, to ensure that there are no other issues that could cause a homeowner to have to call us or someone back out again to in the near future.

A lot of issues can be resolved with regular servicing.

Why Worcester Bosch manifolds fail

Worcester Bosch plastic hydraulic components are designed to handle up to 10 bars worth of pressure.

However upon investigating what was causing manifolds to fail, Worcester Bosch found that in certain circumstances these manifolds were being exposed to pressures much higher than they were designed for.

In some cases these components have been exposed to over 80 bars worth of pressure.