So heard chirping coming from the CO propane monitor. No reason for it I could see. Checked battery voltage ok, fuse ok. Disconnected power then reconnected, Propane red alarm led lit but no buzzer. Pushed the test button, still no buzzer. Removed power and pulled out the unit. Bear in mind the propane is off and the tank out, the heating has been off for 3 months and the Tab door is open. Everything looked fine but the internal battery, rechargeable I think, was dead. It's manufacture date is 2017. The type of alarm I have is obsolete but the replacement type fitting the same hole is available and on order. Since the cost of a new one is less than the gas required to take to my dealer 4.5 hrs away to have him look and maybe replace it along with the loss of time, I just ordered it.
Funny thing is, turns out the chirping was the smoke alarm as the battery needed changing. It's mounted above and I was sure the beep was the CO alarm.
Just as well really. I hadn't tried the CO detector test button since I got the trailer last year. Note to self- test regularly even tho the battery power comes from the trailer.
Manufacturer says change every 7 years or less.
I wonder if there is an easy way to test the actual sensors in it.