Error S.24

Safety precautions:

- If you smell gas: evacuate the property immediately, do not operate electrical switches, call the gas emergency number for your country.

- If a carbon monoxide (CO) alarm sounds, evacuate and call the emergency services or gas emergency service.

- If in doubt, turn off the boiler at the mains switch and the gas cock and call a qualified engineer.

Initial homeowner checks (safe, non-invasive):

1. Check whether a hot tap or shower is actually open. S.24 may simply indicate normal burner operation for hot water demand.

2. Look at the boiler display and icons: is the DHW/tap symbol active? Note any other error codes appearing alongside S.24.

3. Press the boiler reset button once and allow the boiler to restart. Note whether S.24 clears and whether the boiler operates normally thereafter.

4. Check the system pressure on the gauge. Low pressure (typically <1.0 bar) or very high pressure (>2.8–2.9 bar) can cause related faults; restore to the recommended pressure (usually around 1–1.5 bar) following your manual if you know how.

5. Check condensate pipe (external frost exposure): if frozen or blocked the boiler can fault—thaw gently or inspect for obvious blockages.

6. Ensure any room thermostats, cylinder thermostats or external controls (timers, smart controls) are not commanding hot water unexpectedly. Verify Comfort or Frost settings that may keep the boiler firing for DHW.

Further diagnostic checks you can do (observe only, do not dismantle gas or sealed parts):

1. Operate a hot tap while watching the boiler. Does the boiler switch to DHW and fire, then stop when the tap is closed? If yes, the S.24 was likely normal operation.

2. If the boiler fires with no hot water demand, listen for actuator/valve movement when you request DHW or CH (a click or motor sound from the diverter/3‑way valve). If there is no movement when switching between heating and hot water modes, a diverter valve or actuator may be sticking or failed (engineer job).

3. Note any repeating lockouts, fading or flashing flame symbol, or other F‑codes appearing after S.24—these indicate ignition/flame or sensor faults and require professional attention.

4. If the boiler faults after reset and will not provide hot water, record the exact sequence, timings and any other displayed codes or behaviour for the engineer.

What you must not do (and when to call a professional):

- Do not open the boiler casing, attempt to adjust gas valve screws, or replace internal components unless you are a qualified gas engineer.

- Do not attempt electrical diagnostics on the PCB or igniter leads.

When to call a Gas Safe (certified) engineer:

- S.24 persists after reset or returns frequently.

- The boiler fires when there is no hot water demand or will not stop firing.

- Other fault codes appear (F. codes or multiple S. codes), the flame is unstable, or the boiler locks out repeatedly.

- You detect a gas smell or CO alarm activation.

What to tell the engineer when you call:

- Exact model (Vaillant EcoTEC 65kW), the displayed code S.24 and any other codes or symbols shown.

- Whether the code appears only when using a tap or continuously.

- Actions you have taken (reset, pressure check, condensate thawing, photos of the display).

- Any recent work on the boiler or system changes.

Likely professional checks/repairs the engineer may perform (for information only):

- Inspect ignition and flame detection circuitry, gas supply and gas valve operation.

- Check flow/impeller sensor and DHW differential sensors, diverter/3‑way valve and actuator, and pump operation.

- Check condensate trap and flue/venting and ensure no blockage.

- Examine PCB logs and any linked accessory modules for faults.

If the problem is minor and resolved by the safe checks above, you can resume normal use. If the fault persists or you are unsure at any stage, isolate the boiler and book a visit from a registered heating engineer.