Ariston 110 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 110 fault code mean?
Fault code 110 on Ariston boilers indicates that the central heating flow temperature probe has developed an open or short circuit. This probe, known as an NTC thermistor, sits on the heating flow pipe and continuously feeds water temperature readings to the boiler's PCB. When the PCB loses a reliable signal — either because resistance has gone out of range (open circuit) or has dropped to near zero (short circuit) — it cannot safely control the burner, so the boiler locks out as a precaution. The fault applies across the full range of Ariston boiler models and will typically stop both heating and hot water until it is resolved.
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
- Failed or degraded NTC thermistor Common
The flow thermistor changes its electrical resistance in proportion to water temperature. Over time — particularly in older Ariston boilers or those that have never been serviced — the thermistor element can fail internally, producing a reading that is either absent (open circuit) or implausibly low (short circuit). This is by far the most frequent cause of code 110.
- Loose or disconnected wiring at the sensor Common
The two-wire connector at the thermistor body can work loose due to vibration, or may have been disturbed during a recent service or nearby plumbing work. A poor connection mimics an open-circuit sensor fault and will trigger the same code.
- Corroded or damaged wiring loom Sometimes
Persistent condensation inside the boiler casing, a small water leak near the flow pipe, or simply age can cause the wiring between the thermistor and the PCB to corrode, fray, or develop a short to earth. The fault may then appear intermittently before becoming permanent.
- PCB fault misreading the sensor signal Rare
In a small number of cases the thermistor and its wiring test as healthy, but the input circuit on the PCB itself has failed and is misinterpreting the signal. This is less common but should be considered if a known-good replacement sensor does not clear the code.
How to fix it
- Switch the boiler off and wait five minutes before restarting DIY safe
Turn the boiler off at the programmer or its own power switch and leave it completely de-energised for around five minutes. This allows the PCB to fully reset. Power it back on and observe whether code 110 reappears. A single reset is reasonable; if the fault returns straight away, do not keep cycling the power — repeated resets on a persistent lockout can mask a developing problem.
- Press the reset button (once or twice at most) DIY safe
If the boiler has a dedicated reset button — usually marked with a flame-and-slash symbol or labelled 'Reset' — press and hold it for approximately five seconds. Limit yourself to two attempts in total. If the boiler fires and then locks out again within a short time, the underlying fault is still present and needs professional diagnosis.
- Check that your gas supply is working DIY safe
Confirm other gas appliances in the home (hob, gas fire) are working normally, and check that your gas meter isolation valve is in the open position (handle in line with the pipe). A broader gas supply interruption can sometimes cause unusual boiler behaviour, though it is not a direct cause of code 110.
- Visually inspect external wiring without removing the boiler casing DIY safe
With the boiler switched off at the mains, look at any wiring visible at the base or sides of the boiler for obvious signs of damage such as burn marks, pinching, or chafing. Do not remove the boiler casing, pull connectors apart, or touch any internal components — this must be left to a Gas Safe registered engineer.
- Contact a Gas Safe registered engineer to diagnose and replace the thermistor Gas Safe engineer
A qualified engineer will remove the boiler casing safely, use a multimeter to measure the thermistor's resistance at a known water temperature, and compare it against the manufacturer's resistance-temperature curve. If the sensor is out of specification they will replace it — a straightforward job that typically takes under an hour. Ask the engineer to check the return thermistor at the same time, as both sensors are similar in age and wear rate. If a new sensor does not resolve the fault, the engineer will trace the wiring loom and, if necessary, assess whether the PCB requires attention.
Parts you may need
- NTC flow thermistor (Ariston compatible) · from £15
- NTC return thermistor (Ariston compatible) · from £15
- Thermistor wiring harness / sensor lead · from £25
- Ariston PCB (model-specific) · 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–£220, depending on the underlying cause.
Frequently asked questions
Is Ariston fault code 110 dangerous?
Code 110 itself is not a gas safety emergency — it is a sensor fault rather than a gas leak or combustion problem. However, the boiler will lock out and stop producing heat as a precaution, which can become a welfare concern in cold weather, particularly for vulnerable household members. You should arrange for an engineer to attend promptly but there is no need to evacuate the property or call the gas emergency line (0800 111 999) unless you smell gas.
Can I fix Ariston fault code 110 myself?
The reset steps outlined above are safe for a homeowner to try. Beyond that, diagnosis and repair require removal of the boiler casing and use of electrical test equipment — work that should only be carried out by a Gas Safe registered engineer. The thermistor itself is an inexpensive part, but incorrect handling of internal boiler components is both unsafe and, if the boiler is under warranty, likely to invalidate it.
How much does it cost to fix fault code 110 on an Ariston boiler?
For most households the total bill — callout, diagnosis, parts, and labour — falls between £100 and £220 when the fault is a straightforward sensor or wiring issue. The thermistor itself typically costs under £20; the rest is labour. If the PCB turns out to be at fault rather than the sensor, costs rise considerably — a replacement Ariston PCB can be £150–£250 for the part alone, pushing the total to £300 or more depending on the model. Evening, weekend, or bank-holiday callouts usually attract a surcharge of 30–50% on standard rates.
My Ariston boiler is still under warranty — will the repair be free?
Ariston offers manufacturer warranties ranging from two to twelve years depending on the model and registration. If your boiler is within its warranty period and has been serviced annually by a Gas Safe engineer (a common warranty condition), the repair should be covered at no cost. Contact Ariston customer support directly with your boiler's serial number to check your warranty status before booking an independent engineer, as using an unauthorised repairer may affect your cover.
Will an annual service prevent code 110 from recurring?
A Gas Safe engineer carrying out an annual boiler service will check sensor resistance values and inspect wiring connections as part of the routine inspection. Catching a thermistor that is drifting out of specification — or a connector that is beginning to corrode — before it causes a full lockout is one of the most practical benefits of regular servicing. A typical boiler service costs £70–£110 and is also usually required to keep the manufacturer's warranty valid.