How to Fix Ariston 108 Fault Code (Insufficient Water) UK
Ariston 108 means insufficient water. UK diagnosis, parts to order, reset sequence.
What 108 means
Ariston 108 indicates insufficient water. The boiler will lock out and refuse to fire until the fault is cleared.
Do not simply reset — 108 is stored in the Ariston error log and will re-trigger within minutes if the underlying part has failed.
Diagnostic sequence
Enter service mode on the Ariston boiler and read the flow/return/DHW temperatures, fan PWM, ionisation current and pump speed.
Cross-reference against the Ariston technical manual — 108 typically points to two or three candidate parts.
- Check wiring harness continuity to the suspect sensor before condemning it.
- Isolate at the fused spur, discharge and re-inspect connectors.
- Measure resistance / voltage at the PCB plug per Ariston test procedure.
Parts to have on the van
Carry a set of NTC sensors, an ignition electrode kit and a fan for Ariston — these three parts clear >70% of 108 call-outs.
Recommission
After the fix, run the Ariston boiler through a full flow test, gas rate, and combustion analysis. Log to the Benchmark book to preserve manufacturer warranty.
Frequently asked questions
- Can I reset 108 without changing parts?
- Only if the fault has cleared (e.g. low pressure repressurised). Persistent 108 means a hardware failure.
- Which is the most common cause of Ariston 108?
- On Ariston boilers, 108 most often points to the sensor or actuator matching its meaning (insufficient water); check wiring and connector integrity first.
- Is a Gas Safe engineer required?
- Yes — any works past the boiler case seal require a Gas Safe registered engineer under UK law.
Browse boiler spares — 14,820 live parts.
View Boiler Spares