Error S.31

Safety precautions:

1) If you are not competent with gas or mains electrical work do not open the boiler or touch wiring. For any gas-side or internal electrical work call a Gas Safe registered engineer. 2) Before touching wiring, isolate the electrical supply at the fused spur or consumer unit. 3) Always open the gas isolator cock fully before attempting to run the boiler. 4) Do not bypass safety devices; never work on the appliance while gas is turned off unless instructed by an engineer.

Initial checks a homeowner can do:

1) Check the boiler display and menu: confirm it is showing S.31 or 'Summer mode' or 'Heating off'. 2) Check the central programmer/timer: ensure the CH (central heating) program is set to On/Auto for the current time and not set to Holiday or Off. 3) Check the room thermostat: raise the set temperature well above the current room temperature to force a demand. 4) Check radiator thermostatic radiator valves (TRVs): open at least one radiator fully. 5) Check external smart controls or relay boxes: confirm any wireless or wired thermostat is connected and calling for heat. 6) Check boiler settings: often the control panel allows you to select heating flow temperature; make sure it is not set to 'Heating off'.

Simple diagnostic and fix steps:

1) Try switching the heating mode on at the boiler: on most EcoTEC units press the right-hand selector to show heating off, then press the + button to increase the heating flow temperature to a normal value (eg 35-60°C), then press the selector to confirm. If this clears S.31 and the boiler starts normally, the issue was simply the unit set to summer mode. 2) Power cycle the boiler: switch off the mains for 30–60 seconds and switch back on. Observe the display during restart. If the code clears and normal operation resumes, this was a temporary status reset. 3) Verify the boiler receives a CH call: with the programmer and thermostat asking for heat, watch the boiler display — you should see a heating demand indicator and the pump/fan/ignition sequence start. If the boiler shows S.31 despite CH demand being present, suspect the external wiring or a communication fault. 4) Check basic wiring and external controls (only if competent): isolate power, remove the front flap, and inspect the connections to the CH demand terminals. Look for loose wires or corrosion. Re-seat connectors. If you are confident and competent, you can temporarily link the CH call terminals (simulate a call for heat) to test whether the boiler will run — do not do this unless you know what you are doing. 5) Check household fuses/RCD: if the boiler starts then cuts power completely and comes back after a while, check for tripping RCDs, blown fuses or a flaky fused spur. 6) Check that heating system service valves (flow and return) are open and that system pressure is normal. 7) If you have external motorised zone valves or a controller, check their position and supply — a stuck/failed zone valve or failed room thermostat will show as no demand.

When to call a professional:

1) Call a Gas Safe registered engineer if you are unsure, cannot restore heating using the safe checks above, if there are other fault codes accompanying S.31, or if the boiler starts then unexpectedly cuts power repeatedly. 2) Call an electrician or engineer if you suspect mains supply or RCD/fuse issues. 3) If internal wiring, PCB faults, or intermittent communication errors are suspected, these require specialist diagnosis and replacement parts by a trained engineer.

Additional notes:

- S.31 is usually informational (no heat demand) rather than a failure. Start with controls, room thermostat, and programmer settings before assuming a boiler fault. - Never attempt gas-side repairs or internal electronic repairs yourself. Record the exact behaviour, times, and any other codes to give to the engineer; take photos of the display and wiring if safe to do so. - No repair cost estimates are provided; contact a Gas Safe engineer for a diagnosis and quote.