Dad keeps the house at a temperature he picked decades ago, or he turns it down to make a bill smaller, or he stops touching the thermostat because the dial is hard to read. Any of those can leave a house cold without anyone saying a word. The thermostat is where the story starts, so start there.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
What drifts first
Look at the setting, not just the number. Is the thermostat on heat or off, or parked on a level that has not changed in a long time? Is there tape, a cover, or a box over the dial? Is one room cold while the rest of the house is fine? A cold back bedroom usually means the air is not reaching it, such as a closed vent or a door that stays shut, not a failed furnace.
Then look at what he is using instead. A space heater running all day, a cord under a rug, or a heater pushed against a bed or a pile of paper means the house is no longer doing the job and he has started patching it. The heater is the one piece you can test tonight without a tool.
Read the bill and the notices
A cold house and an unpaid bill often arrive together. Find the envelopes. A disconnection notice looks different from a regular statement, and the difference matters because the utility sets the timeline, not you. Ask the company whose name is on the account, who receives notices, and whether a second contact can be added. Write the answers down before you hang up.
What to check, ask, and compare
Check whether the furnace runs at all when the thermostat is set to heat. A unit that does not light, makes a new noise, or trips the same breaker is a repair question for the company that services it, not a settings question for Dad. Ask who holds the service records and when the unit was last looked at. Then compare what he tells you with what the thermostat, the heater, and the bill show. Those three usually disagree first.
Ask Dad how the house feels to him at night, not what the number reads. A man who says it is fine but keeps a coat on indoors has already answered the question.
Your move tonight
Photograph the thermostat with the setting visible, check the space heater cord and the clear space around the heater, and find the newest utility envelope. If there is any disconnection language, call the utility from the number printed on the bill and ask for the account contact, the due date on the notice, and the payment options. Then use Local Help in St. Louis to see who to call for the rest of the week.