Short circuit: Return temperature sensor
The F11 error code on Glow-Worm boilers indicates short circuit: return temperature sensor.
Glow-Worm F11 means: short circuit: return temperature sensor. On this component the documented failure modes are ntc sensor defective, short circuit in the cable harness, cable/casing or the temperature sensor has failed — short circuit or open circuit. You can safely reset the boiler once — if F11 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does F11 Mean
The F11 code is shown by the boiler’s control board when it detects short circuit: return temperature sensor. 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 F11 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 |
|---|
| NTC sensor defective, short circuit in the cable harness, cable/casing |
| The temperature sensor has failed — short circuit or open circuit |
Safety Warning
F11 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
F11 User interface connection fault Check wiring between mainboard and user interface F12 Main board connection fault F13 Main board connection fault Check connection and wires F14 Central heating flow T° > 95°C (203 °F) System f
How to Fix It
Measure the resistance of the temperature sensor with a multimeter and compare it against the manufacturer’s resistance-versus-temperature table; replace it if it is open circuit, short circuit or out of range.
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 F11:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Glow-Worm models | — | Possible |
Frequently Asked Questions
Measure the resistance of the temperature sensor with a multimeter and compare it against the manufacturer’s resistance-versus-temperature table; replace it if it is open circuit, short circuit or out of range. According to the technical documentation, this is the first check on the list for F11.
F11 is not classified as a high-severity fault, so the boiler can be reset once. If F11 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.