The fan does not start at high humidity – what could be the cause?

If a humidity-controlled fan does not start as expected, it may be because humid air is not reaching the humidity sensor. A common cause is cold downdraught in the duct, where cold outdoor air pushes the humid indoor air away from the sensor, preventing it from detecting sufficient humidity. This can be resolved by installing a backdraft damper in the duct to prevent cold air ingress. Alternatively, a louvre vent on the exterior wall can help reduce draught. Both measures allow humid air to remain in the duct long enough for the fan to activate. If you are an end user and are unable to resolve the issue yourself, we recommend contacting the service company that installed the system or the retailer where the product was purchased.