Any of these things may mean water leakage. These are signs of a damp basement. Then check with the manufacturer or its service representative how long such a furnace is designed to last. Copper wiring is safer than the aluminum wiring that is found in many older houses. Check inside the control panel to see whether there are circuit breakers or older style fuse boxes.
Attic insulation is more important than exterior wall insulation.
An attic vent will draw off moisture and will keep the house cooler in the summer. If so, tap the wood to see if it sounds hollow. Check for evidence of insects or rodents by looking inside cupboards and closets for dead insects or mice droppings, or traps and poison bait. Useful checklists and great advice help you prevent or solve many common problemson your own, saving you money and headaches.