24 Volt short-circuit
Check the 24 Volt connection. Remove all plugs with 24 Volt connections such as: fan, pump, any three-port valve and 24 Volt plug to the connecting block.
Check short circuit of disconnected components. Switch on power again to the control unit with the components disconnected. Reconnect the components, which have been checked and are working.
Rectify the short-circuit or replace the short-circuited component.
