I built a room that houses my gas furnace, gas water heater, washer & gas dryer.
I had the CO detector plugged in behind the dryer which is right beside the furnace.
Actually I haven't had one in use now for 10 years.
I think it's time to buy a new one and install it.
One more thing about the furnace pressure switch issues. This same 3 flashes problem happened last year and it always seems to be an issue when we have a heavy WIND event. Wind is not a friend to my furnace operation.
My heat exchange crack was found in the middle of winter. I had to wait 1 1/2 weeks for the part to come from Texas. Nice....keep all the spare furnace parts in Texas during the winter....which Texas doesn't have much of. Probably 90% of the furnaces sold in the country are in the Northeast. Keep the part down south....
And now about my "furnace room."
Insurance companies claim about 90% of house fires start from gas appliances.....so I installed a sprinkler head in the middle of this room which will cover all of these appliances with water coverage.
I got an old liquid type (has a yellow liquid in it that will start to boil and the glass will break opening the sprinkler) sprinkler head from work.
Just ran a tap off the cold water line running into my room.
I did mention my "sprinkler" system to the insurance company. It should knock off a few dollars in your premium payment and it gives you a greater chance of surviving a fire and saving the house.
This is also where I have to install my new CO detector.