Error S.02

Safety precautions:

- Before doing anything turn off the boiler using the front panel controls and isolate the electrical supply at the mains. Do not open the boiler casing while it is live unless you are a qualified engineer.

- If you smell gas, leave the property immediately, call your gas emergency number and do not operate electrical switches.

- If you are not confident working with boilers, wiring or pressurised systems stop and call a competent engineer.

Initial checks a homeowner can do (no tools or simple tools only):

1. Check the boiler display for any additional fault codes or messages that appear with S.02.

2. Check the room thermostat/programmer: is there a call for heat? Set the room thermostat lower and switch the heating to Off to see if the pump stops. Check any smart thermostat or timers as these may be calling the boiler.

3. Confirm summer mode is not active (some models change behavior). Ensure DHW/Heating modes are set as expected.

4. Listen at the boiler: can you hear the pump running? Does it sound normal or strained/noisy? Note whether the pump runs continuously or only for short periods.

5. Check system pressure on the boiler gauge. If pressure is very low (<0.8 bar) or very high (>2.5–3 bar), top-up or bleed as required or consult an engineer; abnormal pressure can indicate leakage or other circulation problems.

6. Check visible pipework and radiator TRVs: are any isolation valves to the pump or flow/return closed? Ensure motorised zone valves are in the open position if applicable.

Basic diagnostic steps you can attempt safely:

1. Reset the boiler: try a single reset using the boiler’s fault-clear button or the control menu. If S.02 clears and stays cleared while the system behaves normally, monitor for recurrence. If it returns immediately, proceed to further checks.

2. Bleed radiators: airlocks can prevent circulation and make the pump run without effective flow. Bleed the highest radiators and then check the boiler pressure and top up if necessary.

3. Check the magnetic filter/strainer (if fitted and accessible): a heavily blocked magnetic filter can restrict flow. If you can isolate and drain the filter following the manufacturer’s instructions, you can clean it, but only if you are comfortable doing so and after isolating the boiler electrically.

4. Observe boiler behavior when heating demand is removed: switch off the thermostat/programmer or set to no demand and see if the pump stops. If the pump continues to run with no demand, it indicates an electrical/control fault rather than a normal call for heat.

If the pump runs when there is no demand or if circulation remains poor after the above checks:

1. Do NOT open the boiler casing if you are not qualified. If you are comfortable and competent: isolate mains power, remove the casing to inspect the pump and wiring for obvious issues (burnt connectors, loose wires, water ingress). Re-secure casing and restore power only as instructed by the manual.

2. A qualified engineer should check: pump motor condition, impeller free movement, pump bearings, pump wiring and relay/PCB outputs, flow/impeller sensor and temperature sensors, and any zone valves or actuators. They will also measure whether the pump is receiving supply voltage when it should and whether the control board is commanding it.

3. If the pump is seized, noisy, or fails to provide flow, the pump will likely need repair or replacement by a professional. If the pump is fine but the PCB is commanding it incorrectly, the electronics or wiring will need professional diagnosis and repair.

When to call a professional (recommended):

- If the pump runs continuously with no heating demand or S.02 returns after reset.

- If there is no heat or hot water even though the pump runs, or if you hear unusual noises from the pump.

- If you are asked to open the boiler casing, perform electrical checks, remove or replace the pump, or investigate gas/combustion components.

- If you cannot isolate or identify a simple cause (closed valve, airlock, low pressure).

Final notes:

- Record the exact error(s) and the circumstances when they occur to tell the engineer (when it runs, any other fault codes, whether resetting helps, thermostat/settings state).

- Only a qualified and registered engineer should perform internal electrical or gas repairs and replace safety-related components. Calling a competent professional promptly avoids further damage and ensures the boiler is safe to operate.