Ariston 201 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 201 fault code mean?
Fault code 201 on an Ariston boiler signals a problem with the domestic hot water (DHW) NTC temperature sensor circuit. The boiler's control board has detected either a short circuit or an open circuit (break) in the wiring loop connected to the hot water sensor, meaning it can no longer get a reliable temperature reading from the DHW side. Without that data, the boiler cannot safely regulate hot water output, so it shuts down and locks out. In Ariston's fault numbering system, the leading digit '2' identifies the domestic hot water circuit as the affected group — so any code beginning with 2 points to the hot water side rather than heating or ignition. Code 201 specifically flags the NTC sensor's electrical circuit as the problem. This is a non-volatile lockout, meaning the boiler will not restart on its own — some form of intervention is needed, whether that's a simple reset or a component repair.
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
- Faulty DHW NTC temperature sensor Common
The NTC sensor itself has failed — either its internal resistance has drifted out of range, or the sensor body has cracked or corroded. This is the single most frequent root cause of code 201, and is usually confirmed when wiring checks out fine but the fault persists.
- Damaged or corroded wiring and connectors Common
The signal wires running between the PCB and the DHW NTC sensor can suffer from loose terminals, oxidised connector pins, or physical damage from heat or vibration over time. A broken connection reads as an open circuit; a pinched or chafed wire can short. Either condition triggers code 201.
- Unstable mains supply or power surge Sometimes
A sudden power cut, voltage spike, or fluctuating mains supply can temporarily confuse the control board's sensor readings, causing a spurious 201 lockout. If the boiler resets cleanly once and does not lock out again, an unstable power supply is a likely contributor. A voltage stabiliser or UPS is worth considering if this recurs.
- Incorrect mains polarity Sometimes
If the boiler's mains supply wiring was connected with live and neutral reversed — for instance after previous electrical work — the control board can misread sensor signals and throw circuit faults including 201. A qualified electrician can check and correct polarity.
- PCB (control board) fault Rare
If the sensor and all associated wiring test healthy, the fault may lie with the PCB itself — either the circuit that powers the sensor reference voltage or the analogue input that reads it. Water ingress, age-related component failure, or a prior power surge can all damage this section of the board.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on the boiler's front panel — on most Ariston models it is marked with a flame symbol or the word 'Reset'. Hold it for approximately 5 seconds until the display responds, then allow the boiler a minute or two to attempt a restart. If it fires up and runs normally, monitor it over the next day or two. If code 201 returns promptly, do not keep resetting — repeated resets without addressing the underlying fault will not help and may mask useful diagnostic information for an engineer.
- Check your mains power supply DIY safe
Confirm that other appliances on the same circuit are working normally and that no fuses or circuit breakers have tripped in your consumer unit. If you have experienced a recent power cut or noticed flickering lights, an unstable mains supply may have triggered the lockout. Restoring a stable supply and resetting once is a reasonable first step.
- Inspect the DHW sensor wiring and connectors — engineer required Gas Safe engineer
A Gas Safe engineer will trace the wiring loom from the PCB to the DHW NTC sensor, checking for loose terminals, corroded or oxidised connector pins, pinched cable runs, and continuity through the circuit. Many 201 faults are resolved at this stage without replacing any components, simply by reseating a connector or replacing a short section of damaged wire.
- Test and replace the DHW NTC sensor if necessary — engineer required Gas Safe engineer
If the wiring tests healthy, the engineer will measure the sensor's resistance at a known water temperature and compare it against Ariston's specification. A sensor reading outside tolerance will be replaced — this is typically a straightforward parts-and-labour job taking under an hour on most Ariston models.
- Diagnose and repair or replace the PCB if the fault persists — engineer required Gas Safe engineer
Should the sensor and wiring both check out, attention turns to the PCB. The engineer will inspect the board for signs of water damage, burnt components, or failed solder joints around the sensor input circuit. A loose PCB connector is a quick fix; a damaged board will need either specialist repair or full replacement. Before authorising a PCB replacement, it is worth asking the engineer to check whether the boiler is still within its manufacturer's warranty, as Ariston warranties range from 2 to 12 years depending on the model and registration.
- Call a Gas Safe registered engineer Gas Safe engineer
If you have not already done so, contact a Gas Safe registered engineer to carry out steps 3 through 5. You can verify an engineer's registration at gassaferegister.co.uk. Provide them with the fault code 201 when booking so they can bring likely spare parts — particularly an NTC sensor compatible with your Ariston model — to save a return visit.
Parts you may need
- Ariston DHW NTC temperature sensor · from £25
- Sensor connector and wiring harness (DHW circuit) · from £20
- Ariston PCB (control 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 £120–£320, depending on the underlying cause.
Frequently asked questions
Can I reset an Ariston 201 fault myself, or do I need an engineer straight away?
You can safely attempt one reset yourself — hold the reset button for around 5 seconds and see if the boiler restarts and stays running. If code 201 reappears within a short time, the underlying fault is still present and repeated resets will not fix it. At that point you need a Gas Safe engineer to inspect the DHW sensor circuit. There is no homeowner-safe way to test or replace the NTC sensor or check the PCB wiring.
How much does it typically cost to fix an Ariston 201 fault in the UK?
For most households the repair falls between £120 and £320 including parts, labour, and VAT. A wiring or connector fix at the lower end, and a sensor replacement with a standard call-out at the higher end, both sit comfortably within that range. PCB replacement is a different matter — a new Ariston control board can cost around £180–£250 in parts alone, pushing the total bill to £350–£500 or more. If your boiler is over eight years old and the PCB is at fault, it is worth getting a new boiler quote alongside the repair quote to compare the long-term value.
Why does the '2' at the start of code 201 matter on an Ariston boiler?
Ariston uses the first digit of its fault codes to indicate which system group is affected. A '2' prefix always points to the domestic hot water (DHW) circuit. This helps engineers narrow down the fault area immediately — if you see any fault code starting with 2, the problem is on the hot water side rather than the central heating circuit, ignition system, or flue. Code 201 specifically identifies the DHW temperature sensor's electrical circuit as the source of the issue.
Could an unstable power supply cause Ariston fault code 201, and is a UPS worth fitting?
Yes — a voltage spike or sudden power cut can temporarily corrupt the sensor readings seen by the PCB, triggering a 201 lockout even when the sensor and wiring are physically fine. If the boiler resets cleanly and runs without issue for weeks or months before the code reappears, an unstable mains supply is a plausible factor. Fitting a voltage stabiliser or uninterruptible power supply (UPS) rated for your boiler's wattage can protect the PCB from future surges. An electrician (not necessarily Gas Safe) can advise on a suitable unit and installation.