Error 200 O

Safety precautions:

1) If you smell gas: do not operate electrical switches or the boiler. Open windows, leave the property and call the gas emergency number immediately. 2) Do not remove the boiler casing or attempt internal repairs unless you are a qualified Gas Safe engineer. 3) Isolate electrical power to the boiler only if instructed by a qualified person. 4) Take care around hot surfaces and hot water; allow the boiler to cool before touching pipework.

Initial homeowner checks you can do:

1) Check the room thermostat and any remote controls/programmer are set to request heat and show the correct time and programme. 2) Confirm the heating zone(s) and TRVs are open. 3) Look at the boiler display: if only 200 O is shown and the radiators are warming, this is normal. 4) Check the system pressure gauge on the boiler: a healthy running pressure is usually around 1.0–1.5 bar (consult your manual for the exact recommended pressure). 5) Walk round the system and check for any visible leaks from radiators, pipes or the boiler.

Simple diagnostic steps and basic remedies:

1) If radiators remain cold but 200 O is displayed, check the timer/thermostat is actually calling for heat (set the room stat higher than room temperature or set the programmer to a heating period). 2) Feel the flow and return pipes at the boiler when it is running (carefully): the flow should be warmer than the return. If the flow is hot and the return is almost as hot, you may have poor circulation or a stuck pump. 3) Bleed radiators that are cold at the top to remove trapped air. After bleeding, re-check system pressure and re-pressurise only if you are comfortable doing so and have the manufacturer instructions; if unsure, call an engineer. 4) If the boiler cycles on and off abnormally or runs for excessively long periods, make a note of when it happens and any other display symbols. This can indicate a thermostat, pump or sensor issue.

When to call a professional:

1) If other fault codes appear in addition to or instead of 200 O, especially codes indicating ignition, sensor, fan or pressure faults. 2) If you cannot get heat or hot water despite controls calling for it. 3) If you find a leak, low or dropping pressure that you cannot safely correct, unusual noises, or repeated lockouts. 4) If you smell gas or suspect a gas leak. 5) If you are not confident carrying out basic checks such as repressurising the system.

Notes and next steps:

1) If 200 O is the only message and the boiler is heating normally, no action is required — this is normal operation. 2) Keep a record (time, what you see on the display, symptoms) to give to the engineer if you do need to call one. 3) Use a Gas Safe registered engineer for any internal repairs, sensor or burner work and for safety-critical checks. 4) Refer to your boiler manual for the exact recommended pressure and any model-specific instructions.