Bob and Tim arrived at their fifth service call of the day. They were both wet from servicing a heat pump outdoor unit in the snow. This was a no heat call for a gas furnace. The weather was cold and there was no heat at all in the house.
In this troubleshooting problem, the customer’s general definition of the situation gets more specific when you arrive at the site and discover that the reason there is no heat is because although the burners ignite on a call for heat, the air handling system never starts, and the system’s limit control shuts the furnace down.