I was installing a propane tank and hooking up my Truma Combi water heater/heater and stove. I figure the step was to install a propane detector. I am installing their combo CO unit , but they have just a propane unit available. Normally I wouldn't think much about posting about this , but I was surprised by the adapter plates that come with the unit. This unit is thin and basically flush mount. The various adapters should cover the hole your original unit had. The replacement date is right on the front of the unit also.
I just replaced mine with one of these yesterday. I wasn't aware that they were supposed to be replaced every five years until I took my old, seven and a half year old unit out. It had started beeping every few seconds and flashing the code that indicated it needed to be replaced.
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Roger
I have a 2007 SMB RB50. My CO detector was the original, no longer made, CCI 3400. I replaced it with this https://a.co/d/gevQdlD Safe-T-Alert by MTI Industries 35-742-BL Dual LP/CO Alarm - 12V, 35 Series Flush Mount, Black.
Fits in the original space and the black looks like it belongs next to the Espar controls (also black).
Just replaced the CO sensor with a date of 1999 (original) with a combo CO/Propane, no LED's light, checked for 12V, but nothing. Some forums mention a fuse, so far, haven't located, i going to check the ground wire to see if it has continuity or if its terminated on a bad location. Any other ideas?