Ariston 202 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 202 fault code mean?
Ariston fault code 202 belongs to the 200-series, which covers domestic hot water (DHW) circuit sensor faults. On most Ariston boilers, code 202 points to a short circuit on the DHW flow or temperature sensor — the component that detects when you open a hot tap and tells the PCB to fire the burner. When this sensor develops an electrical fault, the boiler cannot operate safely and will typically lock out, cutting off your hot water supply. On Evo-range models (Clas HE evo, Clas HE evo System, E-combi evo, and E-system evo), the same code instead relates to a fault with the bottom storage temperature probe, which monitors the temperature in the lower section of a stored hot water vessel. A small number of sources also associate code 202 with a flame detection or ignition lockout on certain variants. Because Ariston applies this code slightly differently across its product range, always check your boiler's specific manual if you are unsure which interpretation applies to your unit.
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
- Short circuit within the DHW flow or temperature sensor Common
The sensor itself has developed an internal electrical fault, causing its resistance to fall outside the range the PCB expects. This is the most direct cause of code 202 and usually means the sensor needs replacing.
- Damaged or loose wiring to the sensor Common
Vibration, heat cycling, and general wear can loosen the connector at the sensor end or cause the wiring to chafe and short against the boiler casing. A break or short in the cable produces exactly the same signal to the PCB as a failed sensor.
- Limescale or debris fouling the sensor housing Sometimes
In hard water areas, limescale accumulation inside the sensor housing can distort readings or physically damage the probe. Sediment in the DHW circuit can have a similar effect, accelerating wear on the sensor.
- Bottom storage temperature probe fault (Evo models only) Sometimes
On Clas HE evo, E-combi evo, and E-system evo boilers, code 202 specifically flags an issue with the probe monitoring the lower section of the hot water store. Wiring faults, a failed probe element, or corrosion at the connector are the typical culprits on these models.
- Flame detection or ignition issue (select variants) Rare
On a small number of Ariston variants, code 202 has been associated with the boiler attempting to light, briefly establishing a flame, and then locking out because the flame signal is not sustained. This can point to a weak spark, a dirty flame sensor electrode, or a gas supply problem.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your boiler's control panel — on most Ariston models it is labelled with a flame and cross symbol or a circular arrow. Press and hold it for approximately five seconds until the boiler attempts to restart. Allow it to complete its ignition sequence before judging whether the fault has cleared. If code 202 reappears immediately or returns within a short time, do not continue resetting, as repeated resets can mask a worsening problem and in rare cases cause additional wear.
- Check that your gas supply is working DIY safe
Confirm that other gas appliances in your home — such as a gas hob or fire — are working normally. If they are not, contact your gas supplier, as the issue may be an interrupted supply rather than a boiler fault. Do not attempt to investigate gas pipework yourself.
- Note the exact boiler model and code variant DIY safe
Find your boiler's model name on the front casing or inside the front panel. This tells you whether you have an Evo-range model (which uses code 202 for the bottom storage probe) or another Ariston model (where 202 means a DHW sensor short circuit). Pass this information to the engineer you contact — it will speed up diagnosis and parts ordering.
- Have a Gas Safe engineer inspect the sensor wiring and connections Gas Safe engineer
An engineer will access the internal wiring loom and check the connectors leading to the DHW flow or temperature sensor. Loose, corroded, or chafed connectors are a common and relatively quick fix. The engineer will also verify that no other components on the same circuit are contributing to the fault.
- Have the sensor tested electrically and replaced if necessary Gas Safe engineer
Using a multimeter, the engineer will measure the sensor's resistance and compare it to the manufacturer's specification. A sensor reading outside tolerance confirms it has failed and must be replaced. On Evo models, the bottom storage probe will be tested in the same way. Replacement sensors are straightforward to fit but require draining part of the system and correctly re-pressurising afterwards.
- Ask the engineer to inspect the PCB if the fault persists after sensor replacement Gas Safe engineer
If a new sensor does not clear the fault, the problem may lie with the printed circuit board (PCB), which processes the sensor's signal. PCB diagnosis and replacement is specialist work and should only be carried out by a Gas Safe registered engineer. This is a less common outcome but worth raising if the initial repair does not resolve the lockout.
- Call a Gas Safe registered engineer Gas Safe engineer
If the boiler remains in lockout after a single reset attempt, contact a Gas Safe registered engineer to carry out a proper diagnosis. You can verify an engineer's registration at gassaferegister.co.uk. Attempting internal repairs yourself on a gas appliance is illegal and dangerous.
Parts you may need
- DHW flow or temperature sensor · from £35
- Bottom storage temperature probe (Evo models) · from £40
- Sensor wiring harness or connector · from £20
- PCB (if implicated after sensor checks) · 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–£300, depending on the underlying cause.
Frequently asked questions
Will Ariston fault code 202 clear itself, or does it need a reset?
Code 202 is a lockout fault, which means the boiler has shut down and will not restart on its own. You can try pressing the reset button once to see if it was a one-off glitch. If the fault returns, the underlying sensor or wiring problem needs to be diagnosed and repaired by a Gas Safe engineer before the boiler will run reliably again.
My boiler is an Ariston Clas HE evo — does code 202 mean the same thing?
Not quite. On the Evo range (Clas HE evo, Clas HE evo System, E-combi evo, and E-system evo), code 202 relates to the bottom storage temperature probe rather than the standard DHW flow sensor. The repair process is similar — an engineer will test the probe electrically and replace it if it has failed — but the probe is located differently, so it is worth telling your engineer which model you have before they arrive.
How much does it cost to fix Ariston fault code 202 in the UK?
For a straightforward sensor or probe replacement, most homeowners pay in the region of £120 to £300 all-in, covering the call-out, labour, and the part itself. If the wiring loom also needs attention the bill may sit towards the upper end of that range. In the less common situation where the PCB is also found to be faulty, costs can rise to £350–£500 or more — but this is not the typical outcome for a code 202 fault.
Is there anything I can do myself before calling an engineer for code 202?
Your options as a homeowner are limited to one reset attempt and confirming that other gas appliances in your home are working (to rule out a gas supply interruption). The sensor, its wiring, and all internal boiler components must be inspected and replaced by a Gas Safe registered engineer. Attempting to access or repair these parts yourself is not permitted under UK gas safety legislation.