Safety switch-off
The F27 error code on Glow-Worm boilers indicates safety switch-off.
Glow-Worm F27 means: safety switch-off. On this component the documented failure modes are moisture on the electronics, electronics (flame monitor) defective. gas solenoid valve leaking, ignition or detection electrode dirty, worn or out of position or wiring, connector or harness of the false flame damaged or loose. A Gas Safe registered engineer should diagnose the root cause.
What Does F27 Mean
The F27 code is shown by the boiler’s control board when it detects safety switch-off. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows F27 and the boiler stops until the fault is cleared |
Common Causes
The first cause below is the one the Glow-Worm service literature publishes for this code (source: boilerfaultfinder.com). The others are the failure modes documented for the same component on other boilers, confirmed by 4 different manufacturers.
| Cause |
|---|
| Moisture on the electronics, electronics (flame monitor) defective. gas solenoid valve leaking |
| Ignition or detection electrode dirty, worn or out of position |
| Wiring, connector or harness of the false flame damaged or loose |
Safety Warning
F27 is a gas-related fault. Never attempt to repair or adjust the gas valve, burner assembly, or flue system yourself. All gas work must be carried out by a Gas Safe registered engineer (UK) or licensed HVAC technician (US). Repeated resets after ignition failure can cause unburnt gas to accumulate inside the combustion chamber — this is a serious safety hazard. If you smell gas at any point, turn off the gas supply at the meter, open windows, leave the property, and call your gas emergency service immediately. Gas-related fault. Do not open the boiler casing or attempt repairs to the gas valve, burner, ignition or flue. Repeated resets are unsafe. Diagnosis and repair must be carried out by a Gas Safe registered engineer.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
1. Note the exact error code and check the manufacturer's installation and service manual for specific guidance. 2. Check all visible wiring connections for security and condition. 3. Power cycle the boiler — switch off at the mains for 30 seconds, then switch back on. 4. If the fault recurs, check the fault history for related or recurring codes. 5. Inspect the boiler for any obvious signs of damage, leaks, or unusual sounds
How to Fix It
Inspect the ignition and detection electrode: clean off any deposits, check the gap and position against the manual, and replace it if it is worn.
Unplug and re-seat the connector of the false flame, then check the harness for chafing, corroded pins and breaks in continuity.
Refer to the Glow-Worm service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Glow-Worm models that can display fault code F27:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Glow-Worm models | — | Possible |
Frequently Asked Questions
Inspect the ignition and detection electrode: clean off any deposits, check the gap and position against the manual, and replace it if it is worn. According to the technical documentation, this is the first check on the list for F27.
F27 is classified as a high-severity fault: it involves gas, combustion or flue components. Do not keep resetting the boiler and do not attempt the repair yourself — call a Gas Safe registered engineer.