F.77Glow-worm
Glow-worm F.77: what it means on your model
Checked against Glow-worm's own documentation: Glow-worm: Energy range fault codes and 1 more source. Last reviewed October 2026. How we check
Engineer only
F.77 means different things on different Glow-worm models. Check the table below against your boiler's model name, which is usually on the front panel or in your user manual.
What you can safely do
There is nothing you can safely do yourself with this one. Leave the boiler off and book an engineer.
Before you book an engineer
- Write down the code exactly as the display shows it: F.77.
- Find your boiler's model name. It is usually on the front panel or in the user manual. The table below shows why it matters: Glow-worm codes can mean different things on different models.
- Note when it started and what the boiler was doing (heating, hot water, or starting up).
- If the boiler is still under warranty, check your warranty paperwork before you book anyone.
Call a Gas Safe engineer if
- Book a Gas Safe registered engineer.
Find a Gas Safe engineer near you
Opens the official Gas Safe Register search.
Applies to Energy range, Betacom A range. Codes can differ between models, so check your manual.