Error S.2

Safety first

- If you are unsure at any stage stop and call a qualified engineer. Working on boilers can be dangerous. Electrical and gas isolation should only be done by competent persons.

- Before any inspection, note the error code and boiler model. You can try simple, non-intrusive checks with the boiler powered on; avoid opening the gas valve or changing sealed components.

Initial checks a homeowner can do

1. Note the exact error and whether the boiler is locked out. Make a note of the boiler pressure on the gauge (cold reading) — target about 1.0–1.5 bar for most systems. Record any recent events (power cuts, bleeding radiators, plumbing work).

2. Check demand and controls: ensure room stat/thermostat and programmer are calling for heat. If no demand, the boiler may not run the pump continuously.

3. Try a simple reset: use the boiler reset button or switch the boiler off at the isolation switch for 1 minute and back on. If the fault clears but returns, further checks are needed.

4. Listen to the boiler when demand is present. You should hear the pump running (a low whir/rumble). If you hear nothing, the pump may not be powered or may be seized.

5. Check visible valves: look at pipework near the pump for two small isolation valves (usually screw-type or lever). Ensure they are open. Also ensure radiator lockshield and TRV valves are not all closed.

6. Check radiators: feel radiators after the boiler has run for several minutes. If they remain cold or only hot at the inlet, there may be poor circulation or an airlock. Bleed a radiator to remove trapped air and see if circulation improves.

7. Check for obvious leaks and the system pressure. If pressure is below ~1.0 bar, repressurise using the filling loop following the boiler manufacturer instructions. After repressurising, run the boiler and see if the S.2 clears.

More specific diagnostics (stop if you are not confident)

1. If the pump does not run but you can hear other boiler components, do not open the boiler casing unless competent. A missing pump sound with power present may indicate an electrical fault, a blown internal fuse or a seized pump. Electrical isolation and testing of the pump supply should be done by an engineer.

2. If the pump runs but flow is poor: try bleeding radiators, open all radiator valves, and check that the system is not blocked (recent works can introduce debris). A persistent lack of flow with the pump running often indicates an internal blockage, a worn pump impeller, or a failed pump (no head pressure).

3. If the system pressure does not change when the pump starts, that is consistent with F.75/flow detection faults. This suggests either the pump is not creating flow or the pressure/flow sensor is faulty. Don’t attempt sensor replacement yourself.

4. If you suspect an airlock: try to balance the system by bleeding radiators from the top floor down and run the pump between bleeds. If you are unfamiliar with the process stop and call an engineer.

When to call a professional

- Call a Gas Safe (or local qualified) engineer if: the S.2 error remains after basic resets, the pump makes no sound, the pump runs but radiators stay cold, you find electrical issues, you need to replace the pump, or you suspect blocked hydraulics or defective sensors. Only a qualified engineer should open the boiler casing, handle gas controls, replace the pump or sensors, test the PCB, or perform advanced electrical diagnostics.

What to tell the engineer when they arrive

- Provide boiler model (Vaillant EcoTEC 65kW), exact error code S.2, current system pressure reading, what checks you have already done (reset, repressurised, bled radiators, checked isolation valves), any recent maintenance or changes, and whether the pump is audible.

Final notes

- Do not try to replace the pump, pressure sensor or electronic components yourself unless you are a qualified boiler engineer. Incorrect work can be dangerous and may invalidate warranties. Use the information above to do safe initial checks and to give clear information to the engineer.