Vaillant ecoTEC 65kW Fault codes & diagnostics

1 fault code with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

System Natural Gas 65 kW 2006-2018 Discontinued
GC Number 41-044-67

Replaced by: ecoTEC plus 48-64kW

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Fault codes

All 1 documented codes

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S.O

Your boiler is working correctly but is currently in standby because it hasn't received a signal from your thermostat to turn the heating on.

Low DIY-safe £0-120

What to check first

  1. Check that your room thermostat is turned up higher than the current room temperature.
  2. Ensure your heating programmer or app is set to an 'On' period.
  3. Replace the batteries in your wireless thermostat if the screen is blank or showing a low battery symbol.

Parts commonly replaced

  • Thermostat batteries
  • Room thermostat
  • External programmer

Related codes

Full explanation for S.O
Status & diagnostic codes

13 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

S.1 Status Your boiler is trying to start up but the internal fan is not spinning properly, preventing the heating from firing up. S.2 Status Your boiler has sensed that water isn't moving through the unit as quickly as it should be, causing it to stop heating to prevent overheating. S.3 Status Your boiler is struggling to light its flame, meaning your heating and hot water will likely stop working soon. S.4 Status Your boiler is currently firing up to provide central heating and is functioning as expected. S.6 Status Your boiler's fan is staying on for too long or running when it should be finished, preventing the next heating cycle from starting safely. S.7 Status Your boiler is struggling to circulate water properly after turning off the heating, which is likely caused by a blockage or a pump issue. S.8 Status Your boiler is temporarily pausing heating because it thinks the house is warm enough or to prevent the system from getting too hot too quickly. S.20 Status Your boiler has received a request to provide hot water but is currently unable to complete the cycle, often because it is already cooling down or busy with another task. S.22 Status Your boiler has detected a problem with the flow of water while trying to heat your taps, which usually means water isn't moving through the system correctly. S.24 Status This is a normal status message indicating that your boiler is currently working correctly to heat your hot water. S.31 Status Your boiler is currently set to summer mode, which means it is only providing hot water and has intentionally ignored the request for central heating. S.34 Status Your boiler has paused because it detects a risk of its internal pipes freezing while trying to heat your home. S.85 Status Your boiler is struggling to move enough water through its system, which is slowing down its performance.