Error 201 O

Safety first

- If you smell gas, hear any unusual gas noises, or a carbon monoxide alarm is sounding: turn the boiler and gas supply off, leave the building, ventilate if safe, and call the gas emergency number and a Gas Safe registered engineer immediately. Do not attempt to investigate inside the boiler.

- Do not remove covers, probes or sensors inside the boiler. Only a Gas Safe qualified engineer should open and work on internal boiler components.

- Switch off electrical supply to the boiler at the isolator before doing any external checks if you need to touch external wiring or controls.

Initial homeowner checks (simple, safe checks you can do yourself)

1. Check whether hot water is actually being used: open a hot tap or shower. 201 O normally appears when there is a demand for domestic hot water. If a tap is on or a programmer/zone is set for hot water, this status is expected.

2. Check the boiler display for any additional symbols or flashing codes (SE, V, B, EA, flashing icons). If other fault codes or flashing are shown, note them and contact a Gas Safe engineer.

3. Check the central heating and hot water programmer/timers and thermostats to confirm a hot water call; ensure the programmer settings haven’t been changed inadvertently (e.g. HW set to on).

4. Check system water pressure on the boiler gauge. Most Worcester boilers should sit around 1–1.5 bar cold. Very low pressure can cause other issues; top up to the recommended pressure if you know how and it’s safe to do so.

5. Listen/observe the boiler when a hot tap is opened: the boiler should attempt to fire and the pump/fan should run. If the display shows 201 O but the boiler does not attempt to fire, note any messages or lack of activity.

Basic reset and observation

1. If the boiler appears to be stuck in that display but you have no hot water demand and no other fault symbols, you can try a single reset: switch the boiler off at the front panel or isolator, wait 30 seconds, then switch back on. Do not repeatedly reset a boiler showing locking fault codes. If the display clears and normal operation resumes, monitor for reoccurrence.

2. If the boiler displays 201 O and is running hot water normally, no further action is needed.

Specific diagnostic steps you can safely follow

1. If 201 O is showing but you have no hot water when a tap is opened: check external controls (hot water programmer, room thermostat, cylinder thermostat). A mis-set programmer or a faulty external control can prevent hot water demand reaching the boiler.

2. For combi boilers: confirm whether the diverter valve appears to be working. Common symptoms of a stuck diverter valve are the boiler running in DHW mode but radiators staying cold, or vice versa. You can test by calling CH and observing whether the boiler switches mode. If diverter valve is suspected, call an engineer — replacement or adjustment is a specialist job.

3. Check for signs of a blocked condensate pipe if temperatures are below freezing (this causes EA-type faults on startup). A blocked condensate can prevent ignition; thaw the external pipe if frozen or call an engineer if blocked.

4. If the boiler shows 201 O but won’t ignite and you hear no fan or burner activity, check mains power and the boiler fused spur. If power is present and the boiler still fails to start, do not proceed further — this may indicate a fan, control board or ignition issue that requires a Gas Safe engineer.

When to call a professional

- Call a Gas Safe registered engineer if: you cannot get hot water despite the 201 O indication; other error codes or flashing symbols appear; the boiler repeatedly locks out; the boiler fails to ignite or you suspect fan, gas valve, sensors or diverter valve faults; system water pressure is repeatedly low without visible leaks; you smell gas or have CO alarm activation.

- Do not attempt internal repairs, sensor replacements, wiring repairs or gas valve work yourself. These tasks must be done by a qualified engineer.

Notes and expectations

- 201 O by itself is usually a normal operating state (hot water mode). Use the checks above to confirm normal operation.

- If after simple checks the boiler continues to behave abnormally, record the exact display and any accompanying symbols or flashing patterns and provide these to the Gas Safe engineer — it speeds up diagnosis.

- For safety and warranty reasons, leave any in-boiler component replacements and sealed-system work to a Gas Safe registered engineer.