If your Worcester Bosch boiler is showing an A1 fault code, the boiler has shut down because it cannot operate safely. This guide explains what the A1 fault code means, what commonly causes it, and when you should stop and call a Gas Safe engineer.

What does the Worcester Bosch A1 fault code mean?

The A1 fault code indicates the boiler has failed to complete a safe ignition or operating sequence. As a safety precaution, the boiler locks out to prevent unsafe operation.

In simple terms:
the boiler is not happy with one or more critical checks, so it refuses to run.

Common causes of the A1 fault code

The A1 fault code can be triggered by several issues, most of which require proper diagnosis rather than guesswork.

Common causes include:

• Ignition failure

• Gas supply interruption

• Faulty ignition electrode

• Internal sensor fault

• PCB (printed circuit board) communication issue

Checks you can do safely before calling an engineer

You can try the following basic checks safely:

• Check other gas appliances (hob or fire) are working

• Check boiler pressure is within the normal operating range

• Reset the boiler once only following the manufacturer’s instructions

• Check reminded error messages on the boiler display

If the fault returns after one reset, do not keep trying.

When NOT to try fixing the A1 fault code yourself

Stop immediately and contact a Gas Safe engineer if:

• The A1 fault code returns after a reset

• Other gas appliances are not working

• You smell gas

• The boiler repeatedly locks out

Internal components, gas valves, ignition systems and PCBs must not be worked on without the correct qualifications.

How the A1 fault code is usually fixed

Once properly diagnosed, common repairs include:

• Ignition electrode replacement

• Gas valve testing or replacement

• Sensor replacement

• PCB diagnostics and replacement

The correct repair depends on testing, not assumptions.

Is it safe to keep using the boiler with an A1 fault?

No.

The boiler has shut down for safety reasons. Repeated resets can cause further damage and delay proper repair.

Need help with a Worcester Bosch A1 fault in Deal or Kent?

If your Worcester Bosch boiler is showing an A1 fault code, our Gas Safe engineers cover Deal and surrounding Kent areas. We can diagnose the issue properly and carry out safe, effective repairs.

Call now or book a boiler repair