Duct Detector INVREP Trouble

I have a Fire-Lite ES-50X Addressable Fire Alarm Control Panel that has two troubles;

RTU 1 - 1M006 - Trouble INVREP
RTU 2 - 1M007 - Trouble INVREP

The duct detectors are System Sensor D4120. There is no module between the panel and the duct detectors.

The detectors are clear and functional, but they are not addressable. Would this cause the trouble? Or is it ok to have an addressable FACP and conventional detectors?

Would just a cut line cause the INVREP trouble?

I appreciate the help

Additional info:
FACP installed 2020

That is most likely the problem. Fire Lite makes addressable duct detectors. Try swapping them out, (and program the panel to look for them)

I agree with @Alex_Wilkinson, the D4120 is a 4 wire Conventional Detector. So you Ethier need Monitor Modules and Control Modules to use it, or replace it with a Firelite D365PL, which is Adressable.

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That’s what I was thinking. We’ll try to install the fire-lite addressable ones

Thank you!

if you’re the end user and not the installer, it sounds like there must have been monitor modules installed at some point to supervise the alarm/trouble contacts of those duct detectors.
Also the fact that they are showing as “M” troubles leads me to believe they were programmed as modules. If all your trying to do is clear the panel, I would recommend install 2 MMF-300 or 2 MMF-301 modules.
Whether you use monitor modules or install addressable duct detectors you will still need SLC at both locations.
Also, if you install addressable duct detectors, the panel will still be in trouble because the addresses 6 and 7 are both programmed for monitor modules. You would have to re-program those points to be duct detectors. Probably supervisory.
Like I asked, I’m not sure if you’re the installer or end user just trying to clear your panel.
Good luck,


The hotel I’m staying in has a Invrep that says Superv Ductp. The panel is MS-9600UDLS and our hotel has 3 floors. I think the room with the trouble response isn’t communicating with the panel. Many different rooms got trouble codes in the past 2 weeks, twice there was a trouble and supervisory at the same time the invrep came. A day or two ago, we had storms so I kept thinking the trouble signal was a ground fault or just another invaild reply. And last week on Monday, our hotel received 9 or 10 alarm signals because a detector activated with no smoke, it could have been a faulty detector. So what is going on here?