Glow-worm Temperature 50 Flashing Fault Code: Causes, Fixes & Repair Costs
What does the Glow-worm Temperature 50 Flashing fault code mean?
When the display on a Glow-Worm Betacom C boiler flashes 'Temperature 50', it is signalling a fault detected on the outside (outdoor) temperature sensor circuit. This sensor — sometimes called a weather compensator sensor — is an optional accessory that, when fitted, feeds external temperature data to the boiler so it can adjust its output for greater efficiency. The boiler continuously monitors the signal from this sensor; if it reads an open circuit, an unexpected resistance value, or no signal at all, it raises the Temperature 50 alert and may limit or stop normal operation until the fault is resolved. Note the wider Betacom C flashing-temperature code series for context: Temperature 30 = central heating thermistor fault, Temperature 40 = domestic hot water thermistor fault, Temperature 50 = outside sensor fault (this page), Temperature 60 = low system pressure, Temperature 70 = air pressure switch fault, Temperature 80 = overheat open circuit, Temperature 90 = flame or gas failure.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Loose or disconnected sensor wiring Common
The most frequent trigger. The cable running from the outdoor sensor back to the PCB terminal can work loose over time, particularly if the sensor is mounted in an exposed location subject to wind or vibration. If recent work has been carried out on the boiler, the connector may simply have been accidentally unplugged and not refitted.
- Corroded or failed outdoor NTC thermistor Common
The outdoor sensor contains a 10 kΩ NTC (negative temperature coefficient) thermistor. Constant exposure to rain, frost, and UV light gradually degrades the sensor housing and the thermistor element itself, causing its resistance to drift outside the range the PCB expects — or to fail open-circuit altogether.
- Boiler configured for a sensor that is not fitted Sometimes
If the boiler's PCB settings were left expecting an outdoor sensor that was never installed, has been removed, or whose shunt/bypass was not fitted, the boiler will raise this fault. This is a configuration issue rather than a hardware failure and is resolved by an engineer adjusting the PCB settings or fitting the correct shunt.
- Damaged wiring harness between sensor and PCB Sometimes
The cable run from an externally mounted sensor can be considerable. Physical damage — from pests, cable staples, or DIY work — or internal wire breakage from repeated flexing can interrupt the circuit and mimic a sensor failure even when the sensor itself is perfectly healthy.
- PCB fault Rare
If the sensor, its wiring, and all connections test within specification but the fault code persists, the PCB's own input circuit for the outdoor sensor may have developed a fault. This is the least common cause but the most expensive to resolve.
How to fix it
- Attempt a boiler reset DIY safe
Turn the central heating control knob to the reset position (the power symbol), hold it for approximately 30 seconds, then turn it back to your desired temperature setting. If the fault clears and the boiler runs normally, monitor it over the next hour. If Temperature 50 returns, do not keep resetting — move on and arrange an engineer visit, as repeated resets without a fix can mask the underlying problem.
- Check that your gas supply is on DIY safe
Confirm other gas appliances in your home (hob, gas fire) are working normally. If they are not, contact your gas supplier rather than an engineer, as the issue is with the incoming supply rather than the boiler.
- Inspect the outdoor sensor visually — do not open the boiler DIY safe
If you can safely access the external sensor unit (usually a small box mounted on an outside wall), look for obvious physical damage: a cracked housing, a cable that has pulled away from its entry point, or heavy corrosion around the cable gland. Do not attempt to open the sensor unit or disconnect any wiring yourself — this observation is simply to relay useful information to the engineer.
- Contact a Gas Safe registered engineer to test the sensor and wiring Gas Safe engineer
An engineer will use a multimeter to measure the resistance of the NTC thermistor at a known ambient temperature and compare it against the manufacturer's resistance-temperature curve. They will also check continuity and insulation resistance along the full cable run from the sensor to the PCB terminal, looking for open circuits, short circuits, or moisture ingress at any junction.
- Engineer to reseat or replace wiring connections Gas Safe engineer
If testing reveals a loose or corroded connector — at the sensor end, at any intermediate junction, or at the PCB terminal block — the engineer will clean, reseat, or replace the affected connection. This is often all that is needed and is a relatively quick job.
- Engineer to replace the outdoor NTC sensor if faulty Gas Safe engineer
Where the thermistor itself has failed, the engineer will fit a replacement outdoor sensor. The sensor is an external component, so no major boiler disassembly is required, keeping labour time modest. The new sensor must be correctly secured and its cable routed to prevent future weather damage.
- Engineer to check and correct PCB configuration if no sensor is fitted Gas Safe engineer
If the boiler was set up expecting an outdoor sensor that is not actually present, the engineer will adjust the relevant PCB parameter or fit the correct shunt across the sensor terminals, as specified in the Betacom C installation manual.
- Engineer to inspect the PCB if all other checks pass Gas Safe engineer
Should the sensor, wiring, and configuration all prove correct but the fault code persist, the PCB's sensor input circuit is suspect. The engineer will assess whether a repair or full PCB replacement is appropriate. This is the most costly outcome, so it is worth confirming the diagnosis thoroughly before proceeding.
Parts you may need
- Glow-Worm outdoor NTC temperature sensor · from £45
- Sensor cable/wiring harness · from £25
- PCB connector/terminal block · from £15
- Betacom C PCB (main circuit board) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£280, depending on the underlying cause.
Frequently asked questions
Do I actually need an outdoor sensor on my Glow-Worm Betacom C?
No — the outdoor sensor is an optional accessory, not a standard-fit component. If you have weather compensation enabled on your boiler but the sensor has failed or was never installed, you will see Temperature 50 Flashing. An engineer can either fit a new sensor to restore weather-compensated operation or reconfigure the PCB so the boiler runs without one, clearing the fault.
Can I just bypass the outdoor sensor myself to stop the fault?
You should not attempt to bypass or disconnect any wiring inside the boiler yourself. While the outdoor sensor itself sits outside, the wiring connects directly to the PCB, and working on boiler electronics without the appropriate qualifications is unsafe and potentially illegal. A Gas Safe engineer can fit the correct bypass shunt in a matter of minutes if that is the right course of action.
How much will it cost to fix the Temperature 50 fault?
For the majority of cases — a loose connection, corroded sensor, or simple replacement — expect a total bill of around £100–£200 including call-out, labour, and parts. If the fault traces back to the PCB, a replacement board typically adds £220–£350 fitted, though engineers will exhaust all simpler explanations first. Prices in London and the South East tend to run 15–25% higher than the national average.
The fault came back shortly after it first appeared — what does that mean?
A recurring Temperature 50 code after a reset almost always points to an active fault rather than a one-off glitch. The most likely culprits are an intermittent connection that warms up and fails again, progressive corrosion inside the sensor, or cable damage that worsens with movement. Stop resetting and book an engineer — repeated resets without a diagnosis will not resolve the underlying problem and could delay a proper fix.