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Need help with Honeywell's wireless Equipment Interface Module (EIM)

3 years ago
last modified: 3 years ago

Our old heat-only thermostat had exactly two wires running to it from the boiler room: red and white (connected to the R and W terminals respectively). It was powered by batteries, which needed replacing every two years or so.
The zone consists of two rooms with different temperatures in them, so we wanted to replace it with a thermostat capable of taking a reading from a remote sensor.

I picked the Honeywell TH8110R1008 Vision Pro 8000.
These radio-using devices require wired-power -- 24VAC -- to talk to sensors so I decided to reuse the existing two wires to supply that, with the signaling done wirelessly. I kept the red wire where it was, but switched the white wire from the W to C-terminal on the thermostat and to the "common" terminal in the boiler room (inside a TACO 406 ZVC). My new thermostat booted and I was able to pair it with an in-house and an outside sensors with ease.

However, it, obviously, could no longer actually turn on the heat.
Honeywell's Equipment Interface Module (EIM) THM5421R1021 IAQ was supposed to help there -- hooked up to the TACO 406 ZVC in the boiler room instead of the thermostat, and talking to the thermostat via Honeywell's proprietary RedLink-protocol.

And that's where I am stuck... Though connecting the wireless sensors was easy, doing the same with the EIM is not working. When the thermostat tells me to "press Connect on the wireless device", I do press the sole button on the EIM, but nothing happens. The EIM's little status light flashes amber, then goes red, and then turns off. Repeatedly...
Thinking, I may have a defective unit, I exchanged it -- but now the replacement is doing the same thing...

Once, when I pressed Connect on the EIM first, the thermostat would not go into "Add a Device" mode complaining of another wireless devices listening -- perhaps, the EIMs are meant to be connected differently from sensors for some reason?

Any idea, what I'm doing wrong? Thanks!

Comments (4)

  • mike_home

    How far apart is the thermostat and EIM? It there anything like metal shielding which could interfere with the wireless signal?

    If there a reception problem you could try bringing the thermostat down to boiler room and temporarily hooking it up to 24V and ground and see if can connect. If that works then you know the devices are working properly but the reception between the two is poor.

  • Elmer J Fudd

    I recently had this pair installed by a contractor as part of an HVAC equipment replacement project. An inability to make the connection as you described was fixed by returning the purchase and getting two new but different units as replacements. I don't know if the problem in the first instance was the EIM or the thermostat but trying again with two different ones solved the problem.

    I can't speak to the right way to wire either unit, that was done by the contractor.

  • doofus

    Ok, it seems, the only way to pair up this thermostat to an EIM is during the former's initial setup. This is the only method, that the EIM's brochure describes, but even the Honeywell tech-support kept telling me, it should connect like any other RedLink device (such as remote sensors), and I should exchange it, if it is not connecting.

    I finally gave up, used the "Reset to Defaults" menu-option on the thermostat and, upon reinitialization, it asked me, whether there is an "Equipment Module" (default answer is "no"). When I said "yes", it told me to press "Connect" on the EIM -- exactly per the EIM's manual.

    Kinda pathetic, that

    • there is no way to connect to EIM after the initial setup is done
    • even Honeywell techsupport (and I was talking to the second-tier guy already) don't know about this...

    But I'm glad it is all working now -- I had to re-connect the remote sensors again, but that was easy in comparison...

  • Elmer J Fudd

    You may be very warranted to to have the reaction you did based on your experience. My take (after about 6 months of use) is the following:

    Thermostats have to deal with a dizzying number of permutations of equipment installations and types having different features and requirements. Honeywell has to deal with all situations but also be easy and usable for HVAC techs and homeowners. I'm going to guess that doing so requires an element of dumbing-down menus and putting in defaults and assumptions to ease the setup process.

    If you want to accuse them of something, I'll join you if you say that these "assumptions" and rigid paths should be better documented. The documentation is also dumbed-down too much. There was one setting in particular I was trying to better understand and get information about and it wasn't to be found. My contractor couldn't answer the question. When I called Honeywell for help, they were a bit dumbfounded too. I ultimately took a shot at what to do and it seems so far to be fine.

    I'm happy with the Honeywell thermostat in operation, especially with the internet gateway. The setup was overall easy, but maybe too easy. My need shouldn't have led me to a dark cul-de-sac with no exit path. Similarly, you shouldn't have run into a situation where if you didn't set up the EIM first thing, there was no obvious way to go back and do it.

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