Error S.00

Safety first: If you are unsure at any stage, stop and call a Gas Safe registered engineer. Do not open the boiler casing or attempt gas or mains electrical repairs unless you are qualified. If there is any smell of gas, evacuate and call your gas emergency number. Work only when it is safe to do so and keep children and pets away.

Initial checks homeowners can do:

1) Check controls and settings: Ensure the room thermostat, programmer/timer and any wireless controllers are set to call for heating now (not in 'off' or 'summer' mode). On the boiler control panel, confirm heating is not set to 'Heating off' or a low flow target (set a reasonable flow temperature, e.g. 55°C). If you have a separate room stat, increase its set temperature above the room temperature to force a call.

2) Look for other status codes: Press the i/info button and note any other S.xx (for example S.30 or S.31) messages which can point to a room thermostat block or summer mode. Record what you see.

3) Check obvious external controls: If you have a programmer, smart controls, or a room thermostat, make sure batteries (if wireless) are good, and that the programmer shows heating is on. If you have radiator TRVs, ensure they are open. Confirm the boiler display shows a heating target when you ask for heat.

4) Boiler pressure: You noted 1.5 bar which is acceptable — if pressure is very low (<1.0) that can prevent heating; if above the high limit it can also block operation.

Specific diagnostic steps and simple fixes you can try safely:

5) Reset the boiler: Use the boiler’s reset/fault-clear key for one second (do not hold it repeatedly). After resetting, set the heating call again and watch the display for changes. Some faults clear after a reset or after the external controller resets following a power cut.

6) Observe behavior when calling for heat: With the heating set to on, put your hand on the boiler pipes (externally, without opening the case) to see if the pump is running (pipes should get warm after a short time) and listen for the pump or valve movement. If you hear nothing and the display stays at S.00, the boiler is not receiving a call or not acting on it.

7) Check for a blocked/latched room thermostat: If the boiler shows S.30 when you press i, that specifically indicates the room thermostat or an external control is blocking heating. Try temporarily bypassing the room thermostat only if you know how to do so safely (for example on simple surface-mounted units you can briefly override to demand heat) — if bypassing makes the boiler fire, the thermostat or its wiring is the culprit. If you are not confident, skip bypass and call an engineer.

8) Check 3-port valve and pump (visual/simple checks only): With the heating called, if you see or hear the motorised valve move (or its lever on older systems) the valve is working. If the valve appears in the hot water position or mid-position and does not move when heat is called, that indicates a valve or actuator fault and an engineer is required. If pipes connected to the pump stay cold while the boiler is calling, the pump may be seized or its electrical supply absent — this also requires an engineer.

9) Consider frost or summer modes: Some boilers will block heating in summer mode or a frost/anti-freeze mode may run intermittently. Verify summer mode is not active on the boiler control and that any frost protection has not latched the unit into a special state.

10) After a power cut: External timers, wireless controls and the boiler’s own PCB can sometimes fail to re-engage correctly. If the problem started after a blackout and simple resets and control checks do not help, this increases the likelihood of an electrical/control fault that needs a professional.

When to call a professional:

- If after the above checks the boiler still shows S.00 and you cannot identify an external control set to off, or if you suspect wiring, motorised valve, pump or PCB faults.

- If other fault codes appear (F.xx) or there are ignition/gas smells, persistent shutdowns, or the pump/valve requires replacement.

- If you are uncomfortable performing any bypass or live checks (do not work on live mains unless qualified).

A competent Gas Safe registered engineer can test the external control volt-free call, confirm 230V supplies where needed, inspect and replace the 3-port valve or pump, and diagnose PCB/communication errors. Explain to the engineer that hot water is working but heating is not and that the S.00 status appeared after a power cut — that information helps narrow the fault. Until repaired, consider temporary measures for occupant comfort (portable heaters, staying with family, etc.) but follow safety guidance for any alternative heating.