ATAG · iC, iS and iR range
118On 2019-onwards i-range boilers: flow and return probe plausibility check failed. On 2015–2018 i-range boilers: system pressure too low (filling needed).
This code applies to iC Economiser, iC Combination, iS System, iR Regular. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Check the pressure gauge with the system cold. On 2015–2018 i-range boilers this code usually means the pressure is too low.
- If it is below about 1.0 bar, repressurise only by following that model's user instructions.
- If the pressure is already in range (typical of 2019-onwards 118), stop resetting and arrange an engineer to test the flow and return sensors.
How an engineer may fix it
On 2015–2018 appliances, check filling, leaks, the pressure sensor and expansion vessel. On 2019-onwards appliances, also test flow and return probe plausibility, position, resistance and wiring before recommissioning.
This list follows the 2019-onwards i-range. On 2015–2018 boilers some codes differ — notably 118, which then meant low water pressure.
Manufacturer source: ATAG — Boiler Troubleshooting (2019 & newer i-range). Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.