How to Fix a Glow-worm F13 Fault

What Does the Glow-worm F13 Fault Mean?

The Glow-worm F13 fault is a main PCB communication fault. It usually means the boiler has detected a problem between the printed circuit board (PCB), sensors or the wiring harness.

As a safety precaution, the PCB shuts the boiler down until the fault has been diagnosed and repaired.

If your boiler is showing a different error, see our full guide to Glow-worm boiler fault codes to understand what each code means.

Is the Glow-worm F13 Fault Dangerous?

The F13 fault is not normally dangerous on its own, but it should not be ignored.

The boiler will usually stop producing heating and hot water until the fault is repaired. Leaving the problem unresolved can result in further component damage and higher repair costs. If the fault appears repeatedly, arrange a repair as soon as possible.

Common Causes of a Glow-worm F13 Fault

The most common causes include:

• A faulty sensor sending incorrect information to the PCB.
• A damaged or loose wiring harness interrupting communication.
• A failed printed circuit board (PCB).
• Loose electrical connections inside the boiler.

Only a qualified engineer can confirm which component has failed.

Can You Fix a Glow-worm F13 Fault Yourself?

In most cases, no.

The only homeowner check worth trying is resetting the boiler.

• Switch the boiler off.
• Turn it back on.
• Press the reset button.
• Wait a few minutes to see if the fault clears.

If the F13 code returns, stop resetting the boiler and arrange a professional inspection. Internal electrical and gas components should only be worked on by a Gas Safe engineer. If the reset doesn't clear the fault, our boiler repair in London service can diagnose and repair the problem safely.

What Affects the Cost of an F13 Repair?

Repair costs depend on the diagnosis, labour time and the component that has failed.

• A faulty sensor may require testing and replacement.
• Wiring or connection faults may involve repair or replacement of damaged components.
• PCB faults can be more involved and should only be priced after professional diagnosis.

A quotation should only be confirmed after diagnosis. On an older boiler with a major component failure, the engineer can explain whether repair or replacement offers better value.

How to Fix a Glow-worm F13 Fault

A Gas Safe engineer will normally:

Step 1 – Arrange a Gas Safe engineer

Book a qualified engineer to inspect the boiler safely.

Step 2 – Diagnose the fault

Test the sensors, wiring and PCB to confirm the exact cause.

Step 3 – Replace faulty parts

Replace any failed components with suitable parts.

Step 4 – Test the boiler

Confirm safe operation before returning the boiler to service.

How Annual Boiler Servicing Helps Prevent Faults

Annual servicing helps identify worn components before they fail. During a service, an engineer checks safety devices, inspects electrical connections, tests boiler performance and looks for early signs of wear. While servicing cannot prevent every F13 fault, it can reduce the chance of unexpected breakdowns.

Need Help with a Glow-worm F13 Fault?

If your Glow-worm boiler is displaying the F13 fault, arrange a professional inspection before the problem gets worse.

Serviceteam's Gas Safe engineers diagnose Glow-worm boiler faults and replace faulty components where needed, helping restore your heating and hot water safely. If your boiler still shows the error after a reset, book a Gas Safe engineer with Serviceteam — we'll identify the cause, explain the repair options and get your heating working again.