Error 202 O

Safety precautions:

1. Do not open the boiler casing or attempt gas or flue repairs yourself. Only a Gas Safe registered engineer must work on gas components.

2. Turn off electrical supply at the isolator before touching any external wiring or controls. Wear appropriate PPE if you inspect pipework.

3. If you smell gas, evacuate the property and call the gas emergency number immediately; do not operate electrical switches.

Initial checks a homeowner can do (non-invasive):

1. Wait. If the boiler has entered anti-cycle, leave it for 15–30 minutes to see whether it clears by itself — this is normal behaviour in many situations.

2. Check the display carefully for any other fault codes or messages and note them down if present.

3. Check your room thermostat/programmer or smart control settings and schedules. Ensure the set temperature is above room temperature so the boiler receives a steady demand and is not being rapidly switched on/off by a faulty schedule or frost/eco function.

4. Check batteries in wireless thermostats or room thermostats and replace them if weak.

5. Check central heating pressure on the boiler gauge — it should normally be about 1–1.5 bar when cold. If the pressure is very low (well below 1.0 bar) top up the system following the boiler handbook instructions.

6. Feel radiators after a boiler run: if some radiators stay cold at the bottom, bleed them to remove trapped air and improve circulation.

7. Listen for the pump running when heating is called — you should hear or feel circulation. If the pump is completely silent when it should be running, record this for the engineer.

Specific diagnostic and simple remedy steps (do not open the boiler):

1. Observe and record the circumstances when anti-cycle appears: what was the demand (hot water, heating), room thermostat behaviour, and how long the symbol stays. This information helps a professional diagnose intermittent control or circulation faults.

2. If pressure is low, repressurise the system to the manufacturer’s recommended pressure (usually 1–1.5 bar) using the filling loop. Follow the boiler manual exactly; only do this if you are comfortable and the filling loop and valves are intact.

3. Bleed radiators to remove air pockets which can cause poor circulation and trigger anti-cycle/gradient limits.

4. If you have zone valves or thermostatic radiator valves (TRVs), check they are not stuck closed and that any motorised valves are calling correctly. Manually operate a zone valve (if accessible) to confirm it moves when the heating is on.

5. Power-cycle the boiler as a last simple step: turn the boiler off via the isolator or front panel, wait 30 seconds, then turn it back on. If the boiler display clears and it returns to normal, continue to monitor. Do not repeatedly reset the boiler if other serious EA/EA-type codes or lockouts appear.

6. If anti-cycle is accompanied by temperature-rising-too-fast messages or very long pause periods, this can indicate a circulation restriction (partially blocked pipe, failed pump or airlock) or a problematic external control. Document frequency and conditions and avoid trying to force internal components to move.

When to call a professional:

1. If the boiler remains in anti-cycle for more than 30 minutes, or anti-cycle returns frequently, or it’s accompanied by other fault codes, you should contact a Gas Safe registered engineer or Worcester Bosch technical support.

2. Call an engineer if you suspect the pump is seized, the boiler regularly locks out, the pressure relief valve is discharging, or you see signs of leaks, overheating, or electrical faults. These require professional diagnosis and safe repair.

Final notes:

1. Anti-cycle is often a normal protective function. Short, occasional pauses are not usually a cause for alarm. Persistent or recurring anti-cycle points to an underlying circulation or control problem that needs an engineer.

2. When you contact a professional, provide the boiler model, the exact error code (202 O), details of when it happens, any other codes shown, boiler pressure, and what checks you have already completed. This speeds diagnosis and helps the engineer bring appropriate parts and tools.