Error 501

Safety precautions:

If you smell gas: open windows and doors, do not operate electrical switches, do not use phones inside the building, turn off the gas at the meter if it is safe to do so, evacuate the property and call the national gas emergency number immediately. If you do not smell gas, proceed with the checks below but do not attempt any internal gas or electrical repairs yourself.

Initial checks a homeowner can do:

1) Note the exact symptoms and error code and how long it’s been showing. Try a single reset of the boiler using the reset button or following the manual. If the fault returns immediately or after a single reset, stop resetting — repeated resets may cause further lockouts.

2) Check other gas appliances (hob, cooker) to see if they work. If all gas appliances are out, check your gas meter or contact your gas supplier.

3) Check the boiler has power: display lit, fuses and RCDs not tripped. Check room thermostat and programmer settings. Ensure the boiler's gas isolation valve (usually a lever on the gas pipe to the boiler) is open.

4) Check the boiler flue and external air inlet visually for obvious blockages (bird nest, debris). Also check the boiler’s condensate pipe in cold weather for freezing — while more commonly linked to other codes, a frozen condensate can contribute to start/firing problems.

Specific diagnostic and next-step checks (still homeowner-level):

1) Listen during a call for heat or hot water: do you hear the fan start, then the ignition spark/clicking? If you do not hear the fan or ignition attempts, that points toward fan, control board, or power problems rather than just the flame sensor.

2) If you hear repeated ignition attempts (clicking) but no sustained burn, this often indicates either lack of gas supply to the burner, a faulty gas valve, or the flame sensor not detecting a flame (dirty/failed electrode). You can try a single reset only to confirm behavior; do not repeatedly reset.

3) Check the boiler pressure gauge. Very low system pressure can sometimes cause the boiler to behave abnormally; top up to the recommended level (consult the manual) if pressure is low, but do not open or disassemble the boiler.

4) If the fault points to a blocked flue/fan (fan not starting or restricted airflow) clear any safe external obstructions and retry. Do not remove or dismantle the fan or flue yourself.

When to call a professional and what to tell them:

If the single reset does not clear the fault, if the fault returns, if the boiler has locked out repeatedly, if you cannot confirm gas supply to the boiler, if the fan does not start, or if you smell gas — call a Gas Safe registered engineer. Do not attempt to replace or test ignition electrodes, gas valves, flame sensors, or any sealed components yourself.

Provide the engineer with: the ATAG model, the exact error code (501), a description of what you heard (fan/ignition clicks or silence), whether other gas appliances work, whether you smelled gas, recent service history, and whether the flue or condensate pipe was frozen or blocked.

Final notes:

This error is a safety lockout and should be treated seriously. Basic checks (reset, gas supply, power, visible flue obstruction) are reasonable for a homeowner, but diagnosis and repair of ignition, gas-valve, flame sensor, fan or PCB faults require a Gas Safe qualified engineer. If in doubt or if you detect any gas smell, immediately follow the emergency gas safety steps and call the appropriate emergency number.