What an annual boiler service actually finds

A boiler can seem to be working fine while a small worn part is quietly causing damage. Here's a real example from a routine service.

Most people book a boiler service because the manufacturer's warranty asks for one, or because a landlord has to. It's easy to think of it as a box-ticking exercise when the boiler seems to be running fine.

This photo is from a routine service. The boiler was heating the house and the customer had no idea anything was wrong. But inside the casing, the flue manifold gasket had worn and was leaking.

Why that matters

Condensing boilers produce acidic condensate as part of normal running. It's meant to drain away safely. Here it was escaping inside the boiler instead, and over time it would have eaten through the casing. That's the kind of damage that can turn an economical repair into a replacement boiler.

The same worn gasket was letting combustion products escape inside the casing, where they could be drawn back in with the air the burner uses. A boiler needs clean air to burn properly, so that's not something to leave.

The fix

A new gasket, fitted during the service. A small part, caught early, before it caused damage that couldn't be undone.

What a proper service includes

A service isn't just a quick look and a sticker. It means opening the boiler up, checking the seals and gaskets, cleaning where needed, and testing that the boiler is burning safely and efficiently.

If your boiler hasn't been regularly serviced, book a service.