Tstat8 MSTP Heating Valve stuck closed

Apologies in advance for the info dump.
I am having an issue with a Niagara front end connected via MSTP to Tstat8 stats. The stats work well for a while but after 1-3 days I will find a handful of the 19 total in the building have the 2 position NO heating valve continuing to receive 24v volts even when there is a call for heat. The MSTP points from the stat within the Niagara indicate the valve should be opening, but it is still receiving 24v at the valve.

I haven’t connected via the T3000 software while this issue is active as to discover the stat I’ve been using the bottom plugin and I’ve had to change protocol back to Modbus and unhook the MSTP network. When I reboot the stat the valve opens upon call for heat appropriately.

This is a newly installed/commissioned project and is widespread but inconsistent among the stats/heating valves. My next troubleshooting plans are to be unhook the stats from the Bacnet router and see if the issue reoccurs, and attempt to hook up via T3000 software while the issue is occuring.

The Heating Valve is hooked up to K5 / output 5.
Baud rate is 19k.
Stats had their firmware updated during my last visit to the site and still having the issue.
Uncertain if there is something with the BACnet points or MSTP network that is causing this issue. We are having some MSTP network issues with brief drops and the only thing on this network are the stats. Bacnet router is middle of line with resistors at the ends. Included some snips of call for heat and network diagnostics.

Interested if you have had any similar issues with outputs getting stuck before. particularly on MSTP networks.


It would really help to see what is going on from the T3000 front end. If that’s not possible perhaps you can use a generic bacnet tool like Yabe to show the input/output states and any other bacnet variables you can pull from the device. I will have our team check through your screen shots to see if we can pick up anything. It could be something like the override timers… just a guess but it sounds like something which is temporarily holding the unit into a mode it should not be in.

Apologies for the delayed response, I am now back on site at the project for the next few days.

Not having any luck adding the device to T3000 as it is in Bacnet protocol and I don’t have a true project in the software / know how to add as a bacnet MSTP device. I’ve only added the Tstat8s as modbus to T3000 for firmware update.

I did pull up the bacnet points and am including a snip from my tool of the DO1 (I’m seeing overridden and out of service check boxes marked) and then a Niagara points table .txt that includes all points and current configuration.
I do see a transaction timeout on the OvrdTimer. Uncertain what that indicates or could effect.

This stat is registering a call for heat and is attempting to turn on the fan at DO5 (we have CUHs on some of these but not all) and the DO1 appears to be false allowing the valve to open but the NO heating valve wired to K01/DO1 is still closed / receiving 24v.
Let me know if there is other information I can provide that would be helpful.

Tstat8 MAC5.txt (8.5 KB)

The T3000 view of the output is hidden there. There are a few devices online by the looks of it. I am not clear if those devices are in bacnet or modbus mode but you can test either protocol with the T3000 modbus tool or the bacnet tool as appropriate. Once you have that working we can graduate on to integrating with Niagara, I would leave that for last.

Here you go. I’m expecting DO1 to be off when there is a call for heat.
It does when I reset the stat, but then after a while it gets into this situation where DO1 stays On.
Let me know if there are other screenshots you need.

Not working as expected:

Working as expected:

I see what you mean, the PIDs are both showing 0% which is 100% heating action. The working mode has output 1 on and the not working mode has output1 off. There are some interlock features in the output tables, if we could see the output config table that would help us see if they are tripping something up here by chance.

I will have a member of our team check all this over. You could email your config file to register3 (at) temcocontrols (dot) com and I’ll make sure he gets it. You can save the config file by navigating to T3000 → file → save-as.