Error C

Safety precautions:

1. If you are unsure about any step, stop and call a Gas Safe/RGII qualified engineer. Do not open the boiler casing or work on gas or main electrical connections yourself.

2. Only carry out external checks and simple controls adjustments. Never tamper with internal boiler parts, gas valves, ignition components or PCB circuits.

Initial checks a homeowner can do:

1. Look at the boiler display and confirm it shows C. Note whether the burner-on indicator is illuminated when you expect heat.

2. Check the room thermostat and programmer: ensure the programmer is set to call for central heating or hot water at the current time and the room thermostat is turned up above the room temperature.

3. Check the boiler mode knob: set to BOILER ON and ensure the radiator/tap symbols read Ready or On as appropriate.

4. Check the central heating temperature knob on the boiler: if it is set low, increase it (the manual recommends MAX for cold spell). Flow temp can be up to 80°C; radiator approx. 30–80°C depending on the knob position.

5. Check system pressure on the gauge (behind the drop-down door). It should be around 1–1.5 bar when cold. If pressure is low, top up via the filling loop following your manual before proceeding.

6. Bleed radiators if some are cold at the top. After bleeding, re-check and re-pressurise to about 1–1.5 bar if required.

Specific diagnostic steps and simple fixes:

1. Force a call: increase the room thermostat or set the programmer to a continuous ON/override mode and confirm the boiler receives a demand. Watch the display: if the boiler switches from 00 to C or to a running code and the burner lights, it was simply at set temperature before.

2. Raise the boiler CH temperature control: if the boiler then fires and radiators heat, the original setting was too low for your heat requirement — leave it at the higher setting or adjust the programmer/thermostat instead of permanently maxing out.

3. If the boiler shows C but the house is still cold and the boiler does not attempt to fire when you force a demand, check the external controls: ensure programmer, room thermostat and any cylinder stat are all calling for heat and their wiring/ batteries (if applicable) are OK.

4. If the pressure is below 1.0 bar, repressurise the system to ~1.3 bar and restart the boiler. Low pressure can prevent normal operation.

5. Press the RESTART button on the boiler to repeat the ignition sequence if you made adjustments — follow the manual instructions for restart.

6. Listen and observe: if the pump runs briefly then the boiler goes to C, there may be insufficient heat demand because a thermostat/ programmer is satisfied or a valve is closed. Check radiator valves, zone valves and motorised valves (if present) to ensure they are opening when CH is called.

When to call a professional:

1. Call a Gas Safe/RGII engineer if the boiler continues to display C while you have a confirmed demand for heat and the boiler does not fire after the checks above. This may indicate a faulty temperature sensor (flow or return thermistor), a control/PCB issue, or a problem with external controls or wiring.

2. Call a professional immediately if other fault codes appear, the boiler locks out, there is a gas smell, water leaks, or if you are uncomfortable performing the basic checks.

Summary note:

The C code usually means normal operation — the boiler thinks it is at the desired set temperature. Start by checking programmer, room thermostat, boiler temperature knob and system pressure. Only simple user-level adjustments are recommended; any internal inspection, wiring work or repairs must be done by a qualified engineer.