Ariston 116 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 116 fault code mean?
Ariston fault code 116 points to a problem with the room temperature sensor circuit or, on certain models, an open floor thermostat circuit. The boiler has detected that the signal from the room sensor (NTC) is missing or out of range — either because the sensor has failed, the wiring has lost continuity, or the circuit has opened. On most modern Ariston combis and system boilers this is a room temperature sensor fault (similar in nature to code 114, which covers the outdoor sensor). On some older models such as the Clas HE R, the code specifically flags a floor thermostat contact open condition, meaning the underfloor heating thermostat circuit is not completing properly. In both interpretations the boiler may refuse to fire for heating until the circuit is restored, but this is not a gas safety emergency.
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 wiring at the room sensor Common
The most frequent trigger. Vibration, age, or a DIY disturbance to the wiring at the sensor head or terminal block can cause the circuit to drop out intermittently or permanently. The boiler interprets the open circuit as a sensor fault and raises code 116.
- Faulty room temperature sensor (NTC) Common
The NTC sensor itself can degrade over time, drift out of calibration, or fail outright. When resistance readings fall outside the expected range, the boiler logs the fault rather than risk running on bad temperature data.
- Open floor thermostat circuit (underfloor heating models) Sometimes
On Ariston models configured for underfloor heating, a floor thermostat that has opened — due to an air pocket in the UFH pipework, a tripped safety stat, or a wiring break — will cause code 116. The boiler sees the open circuit as a fault rather than a normal off signal.
- Damaged or shorted sensor cable Sometimes
The cable running from the boiler PCB to the room sensor can be pinched, chafed, or affected by moisture, causing a short or open circuit that mimics a sensor failure. The fault may appear intermittently if the damage is partial.
- PCB fault or corrosion Rare
If wiring and the sensor both test correctly, corrosion or damage on the PCB's sensor input terminals can produce a false 116 reading. This is relatively uncommon but is more likely on older boilers or those installed in damp environments.
How to fix it
- Reset the boiler once DIY safe
Press and hold the reset button for approximately five seconds until the boiler attempts to restart. A single reset is worthwhile as code 116 can occasionally be triggered by a temporary signal glitch. If the fault clears and stays away, monitor the boiler over the next day or two. If code 116 returns, do not keep resetting — repeated resets will not fix an underlying wiring or sensor problem and can mask deterioration.
- Check your room thermostat or sensor head DIY safe
If you have a wired room thermostat or a plug-in sensor, check that it is firmly seated in its wall plate and that no wires are visibly loose at the back. Make sure the thermostat has power (display lit, batteries not flat). Do not open the boiler casing — just inspect the thermostat end of the circuit, which is a standard household item.
- Check the floor thermostat if underfloor heating is fitted DIY safe
If your system includes underfloor heating with a dedicated floor thermostat, locate the thermostat and check it is set to an appropriate temperature and has not tripped. Some floor stats have a small reset button. Check the wiring at the stat is secure. If you suspect an air pocket in the UFH circuit is holding a safety stat open, bleed the UFH manifold following the UFH manufacturer's guidance.
- Inspect sensor wiring back to the boiler (engineer) Gas Safe engineer
A Gas Safe engineer will trace the wiring from the room sensor terminal on the PCB back to the sensor head, checking for breaks, corrosion, or loose connections at both ends. Any damaged cable sections will be repaired or replaced at this stage.
- Test the sensor circuit with a multimeter (engineer) Gas Safe engineer
The engineer will measure resistance across the NTC sensor at the boiler's terminal strip and compare it against Ariston's published resistance-temperature curve for that sensor type. A reading outside tolerance confirms the sensor has failed and needs replacing. A correct reading shifts suspicion to the wiring or PCB.
- Replace the room temperature sensor or thermostat (engineer) Gas Safe engineer
If the sensor tests faulty, the engineer will fit a compatible replacement NTC sensor or room thermostat, restore the wiring, and clear the fault. This is typically the most common and most cost-effective resolution for code 116.
- Investigate or replace the PCB if all other components test correctly (engineer) Gas Safe engineer
Should the sensor and all wiring prove sound but code 116 persists, the fault likely lies on the PCB's sensor input circuitry. The engineer may attempt to clean and reseat the relevant connectors first; if that does not resolve it, a PCB replacement will be required. This is the most expensive outcome and is relatively rare for this fault code.
- Call a Gas Safe registered engineer if the fault has not cleared Gas Safe engineer
If code 116 returns after your reset and any accessible checks above, book a Gas Safe registered engineer to carry out a full diagnosis. Internal boiler wiring, component testing, and any part replacement must be done by a qualified professional. You can verify an engineer's Gas Safe status at gassaferegister.co.uk.
Parts you may need
- Room NTC temperature sensor · from £25
- Room thermostat (wired replacement) · from £45
- Floor thermostat · from £35
- Sensor wiring loom / cable · from £20
- Ariston PCB (model-dependent) · 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
Is Ariston fault code 116 dangerous — do I need to turn the boiler off immediately?
No, code 116 is not a gas safety emergency. It relates to a sensor or thermostat circuit rather than a gas or combustion problem. Your boiler will typically stop providing central heating but may still operate hot water in some configurations. You do not need to shut the boiler off at the gas supply, but you should arrange for a Gas Safe engineer to investigate if one reset does not clear it.
Can I fix Ariston fault code 116 myself?
The only homeowner-safe actions are: attempting one boiler reset, checking that your room thermostat is powered and properly seated on its wall plate, and — if you have underfloor heating — checking the floor thermostat has not tripped. Any work inside the boiler casing, testing components with a multimeter, or replacing a sensor must be done by a Gas Safe registered engineer. Fault 116 does not involve gas components, so it is not a legal restriction, but incorrect wiring work can introduce new faults or create electrical hazards.
How much does it typically cost to repair Ariston fault code 116 in the UK?
For the most common resolution — a wiring repair or room sensor replacement — expect to pay roughly £100–£280 including parts and labour. Simple reconnection of a loose wire at the lower end; a new NTC sensor plus an engineer's time at the higher end. If the fault turns out to be a PCB failure, costs rise significantly, often £350–£600 or more depending on the model and your location. London and the South East tend to attract higher labour rates than other regions.
Why does my Ariston show code 116 even though I have a wireless thermostat?
A wireless thermostat communicates with a receiver wired into the boiler. Fault code 116 can still appear if the wired connection between the receiver and the boiler's PCB becomes loose or corroded, if the receiver itself develops a fault, or if the boiler is also configured to read a separate room NTC sensor independently of the thermostat. An engineer will check the receiver wiring and any additional sensor circuits to identify exactly where the open circuit is occurring.
What is the difference between Ariston fault codes 114 and 116?
Both codes flag a sensor circuit problem, but they cover different sensors. Code 114 means the boiler has lost contact with the outdoor temperature sensor — typically used for weather compensation on systems with an external probe fitted to an outside wall. Code 116 means the boiler has lost contact with the room temperature sensor or floor thermostat circuit. The diagnostic approach is similar for both, but an engineer will inspect different wiring runs and components depending on which code is displayed.