Error 203

Safety first

1. If you smell gas, leave the property immediately and call the gas emergency number. Do not touch electrical switches or the boiler controls. Call a Gas Safe engineer.

2. Do not attempt internal repairs on the boiler or access gas valves, burners, or seals. Only perform external checks and user-level controls. If you are unsure, stop and call a professional.

Initial homeowner checks you can do

1. Check the boiler display and lights: note the 203 code and whether any other symbols or fault codes appear. Press the spanner/return (info) button to view any three-digit cause code shown in the information menu — write this down for an engineer if needed.

2. Check mains power: ensure the boiler is switched on at the fused spur and the display is lit.

3. Check the central heating programmer/timer: make sure CH or DHW is scheduled to be on, and that you haven’t accidentally set the boiler to Off, Holiday, or Economy mode.

4. Check room thermostat settings: raise the room stat or set the thermostat to a higher temperature than the current room temperature to demand heat. If you have a wireless or smart thermostat, confirm it is powered, connected and calling for heat.

5. Check hot water settings: if you need hot water, make sure the HW mode is on and any cylinder thermostat is allowing demand.

6. Check system pressure: look at the boiler pressure gauge. Typical cold system pressure is around 1–1.5 bar. If pressure is very low (below ~0.8 bar) the boiler may not fire; follow your manual to re-pressurise or call an engineer if unsure.

7. In cold weather check the condensate pipe for freezing (external plastic pipe). A frozen condensate can cause blockage/lockout; if frozen, thaw gently with warm (not boiling) water and check if the boiler clears the condition.

Specific diagnostic steps and simple fixes

1. Create a demand: set the programmer to call for central heating and raise the room stat. Watch the boiler for 1–2 minutes to see if it starts sequence (pump/fan noise, display changes). If it starts, the 203 standby was normal.

2. If the boiler does not respond to a clear demand: check batteries in wireless thermostats or any room stat. Replace and try again.

3. Check external switching contacts: if you have external controls (e.g., time switch, zone valves, smart heating controller), ensure they are not telling the boiler to go to standby. Temporarily bypassing external controls should only be attempted if you understand the wiring—otherwise record settings and call an engineer.

4. Press the reset button once only if the boiler shows no other fault besides standby and you expect it to run. Wait and observe — do not continually press reset. If a locking fault appears after reset, stop and contact a Gas Safe engineer.

5. Use the boiler info menu (spanner/return) to read any cause code. If a cause code other than 203 is shown, note it and refer to the manual or give it to the engineer. Many blocking or locking issues will show a cause code that helps diagnosis.

6. Allow for anti-cycle/gradient limit conditions: some Worcester boilers pause firing for a few minutes if the flow temperature is already at or above setpoint or during anti-cycle protection. Wait 10–30 minutes to see if the boiler clears by itself.

When to call a professional

1. Call a Gas Safe registered engineer if:

- You expect heat or hot water but the boiler remains in standby after checks and reset.

- Other fault codes, warning triangles, or locking/blocking conditions appear.

- System pressure is low and you cannot safely re-pressurise or pressure keeps dropping.

- The boiler starts to show intermittent behaviour, repeated lockouts, or strange noises.

2. When you call, give the engineer the model (Worcester Bosch GB162), the displayed fault code (203), any cause code from the info menu, and a clear description of what you’ve already checked.

Final notes

203 is usually not a serious fault — it most often means the boiler is simply not being asked to fire. Use the checks above before involving an engineer. Do not attempt internal repairs, open the boiler casing or work on gas or sealed electrical parts; leave those tasks to a Gas Safe registered professional.