If DHW priority is selected then heat to the heating system is stopped during a call for DHW. At cold outdoor temperatures the building may freeze up when there is a long call for DHW. In order to prevent this, the control must be able to override the priority and simultaneously operate the heating system and the DHW. The maximum time allowed for DHW priority should decrease as the outdoor temperature drops. This function provides more comfort by preventing large temperature drops in the space during DHW operation.