Error S.1

Safety precautions:

- If you smell gas, leave the property immediately and call the gas emergency number. Do not operate electrical switches or the appliance.

- Isolate electrical power to the boiler before any physical inspection by switching off at the fused spur or consumer unit.

- Never remove sealed covers, alter gas or flue components, or attempt internal electrical repairs unless you are a registered Gas Safe engineer (or local equivalent).

Initial checks a homeowner can do (safe, non-intrusive):

1) Note the display and any additional fault codes. Write down S.1 and any F or S codes shown, and the time/date they occur.

2) Try a controlled reset: switch the boiler off, wait one minute, switch back on and allow the boiler to attempt a restart. If the fault does not recur, monitor for repeats. If S.1 returns immediately or repeatedly, proceed to next checks.

3) Check external flue and air intake: look for bird nests, leaves, debris, or snow/ice blocking the flue terminal or air intake. Clear obvious external obstructions only if safely reachable from the ground or with safe access.

4) Check around the boiler for signs of blocked condensate drain or water around the flue way. A blocked condensate trap or external pipe frost can sometimes affect safe operation—clear minor external frost/ice if safe to do so.

5) Ensure the boiler has correct power and no tripped RCD/MCB or blown fuse in the house. Confirm other mains appliances work.

If initial checks do not fix it (what a qualified engineer will typically do):

- If the fault persists, call a qualified Gas Safe engineer and provide: boiler model (Vaillant EcoTEC 65 kW), exact fault code S.1, how often it happens, and what you have already checked.

What the engineer will typically check and fix (for information):

- Verify error history and operation in service mode, and confirm fan start attempts.

- Check for external and internal flue blockages and confirm flue terminal integrity.

- Test fan electrical supply and earthing, inspect connectors and wiring harness for loose, corroded or damaged plugs (including fan plug and PCB connections).

- Inspect and test the fan motor and hall/rotation sensor. Replace the fan assembly if motor or sensor is faulty or seized.

- If wiring and fan are good, the engineer will test the PCB and related electronics; intermittent or implausible fan signals may indicate a control board fault that could require replacement.

- After any repair, the engineer will perform a controlled run and safety checks to ensure correct flue flow and safe combustion, and will reset and clear the fault memory.

Final notes and recommendation:

- Because S.1 prevents safe flue operation and ignition, treat it as a priority fault. If a simple reset and external flue/air intake check do not cure it, stop trying to run the boiler and book a Gas Safe qualified engineer. Provide the exact fault code and any observations (noises, smells, whether the fan hums) to speed diagnosis. Do not attempt internal repairs or replacements yourself.