ACHR News reported that DiversiTech has added a CO shutoff switch to its safety portfolio, describing the CO/PRO device as one that "interrupts power to the connected equipment" when carbon monoxide is elevated. The source is ACHR News's report on DiversiTech's CO shutoff switch. The story describes the device. It does not describe what a homeowner sees when the device does its job, and that is the part worth planning for.
When a shutoff works as designed, the furnace goes dark. In a cold house, the first thing most people do is reset the switch or breaker and try again. A single reset may be harmless, but repeated resets erase the evidence a technician needs and can keep a real problem running in the background. Treat the trip as information first and as an inconvenience second.
Write the Event Before the Reset
Before you touch anything, capture the state of the house. Note the time, the thermostat setting, and whether the heat call light was on. Check the outdoor temperature and whether snow, ice, or leaves are piled around the vent termination or the combustion air openings. Look at any indicator on the furnace or air handler cabinet and write down exactly what it shows. If a household CO alarm sounded, record which unit, where it is mounted, and what its display said.
Then list anything that changed in the last few days. Ask yourself whether the dryer vent was cleared, a new appliance was installed, a fireplace or space heater ran longer than usual, or a vehicle was warmed up in an attached garage. A shutoff reacts to a threshold being crossed. It does not tell you why, so your list of changes is often the fastest path to the source.
Map the Power Path
Find the breaker or disconnect that feeds the furnace or air handler, and label it if it is not already labeled. A homeowner with a multimeter can confirm the basics without opening gas components. With the cabinet closed and the equipment switched on, you should read line voltage at the disconnect. At the thermostat, a call for heat should show about 24 volts AC between the R and the common terminal on the wall plate. If the voltage is present at the thermostat but the equipment stays off, the trip is upstream of the control board, and you can say so precisely when you call.
Shut the power off before you open any panel, and keep your hands out of the gas valve and burner area. Your job is to gather readings and facts, not to repair the combustion side. If a reading does not match what you expect, write the number down and leave the fix to the service company.
Keep the Sheet With the Equipment
Create one page for each trip. Include the date and time, the outdoor temperature, the thermostat setting, the cabinet indicator, your voltage readings, every action you took, and the name of the person you called. When the technician arrives, add what they found and what they replaced or reset. Tape the sheet inside the furnace closet or file it with the equipment paperwork so the next visit starts from a complete record.
The shutoff tells you that something crossed a threshold. It does not tell you where the gas came from, and it does not clear the cause. Your sheet keeps the story intact until someone qualified closes it out.
If an Alarm Is Sounding
If any household CO alarm is sounding, do not treat it as a nuisance to silence. Move everyone outside to fresh air, leave the door open behind you, and call the fire department or your utility from outside the house. Do not restore power to the furnace to see whether the heat comes back. Let the responders and a qualified technician decide when the equipment is safe to run.
A furnace that stays off on a cold night is an annoyance you can plan for. A furnace that trips for a reason nobody wrote down is harder to diagnose and easier to restart by mistake. Keep the sheet, label the breaker, and make the first call with facts in hand.