Boiler faults

Boiler faults tell you something is wrong.

Boiler fault codes are a boilers way of telling us what has gone wrong. A boiler breakdown can be a massive problem. We rely on our boilers (especially combi boilers) more than we realise not just in the winter to provide hot water and heating. Luckily boiler fault codes give us a clue about why the heat and hot water aren’t working.

What is a boiler fault code?

The boiler follows a set sequence of operations as it runs. A rough example may be like this:

The boiler checks the water pressure
The boiler runs the pump and checks the water is moving.
Checks the temperatures in the boiler.
Runs the fan and checks it is spinning fast enough.
Opens the gas valve and tries to ignite the gas.
Checks to see if the gas has ignited.

As it goes through its sequence it is looking for readings from sensors that fit with its expectations. If the readings are as expected the boiler carries on. If they aren’t as expected the boiler stops and displays a fault code.

Boiler fault codes can be annoying but they are designed to keep you and your family safe, inform you of potential problems and avoid unnecessary damage to the boiler.

A Vaillant home combo displaying an f29 fault code — A Vaillant home combi displaying an f29 fault code

What does a fault code look like?

Most modern boilers have a digital display which can show a series of digits to indicate the fault type.

Boilers that don’t have a digital display use a series of lights that flash in a sequence or have an on or off pattern that shows the fault.

Each manufacturer has its own set of fault codes. Some are shared between models others are specific to that particular model.

My boiler is broken but there is no fault code

This type of fault comes when the sequence of operation isn’t broken but the boiler still doesn’t go to a fault.

If there is a problem with controls or the plumbing side of your central heating the boiler won’t know about it so won’t develop a fault.

If the fault isn’t quite serious enough (yet) to break the sequence of operations then there will be no fault code. This type of fault needs a different type of fault finding.

If the fault is on the control board (PCB) it may not develop a fault but still not work.

Click here for more advice on faults that don’t show a fault code.