Could a loose wire cause Worcester Boiler Error 1019?

Absolutely. Loose or disconnected wires are a frequent culprit for communication errors like Error 1019. Inspect all wiring connections to the boiler, thermostats, and any other connected devices. Ensure that wires are securely fastened and that there are no signs of damage, such as frayed insulation. Carefully tighten any loose connections, but avoid forcing anything.