Horstmann HRT4-ZW Thermostat – open ends

A few weeks ago I received an e-mail from a guy who rather stays anonymous, but had some really great additional/detailed information about the HRT4-ZW thermostat.
There’s some things I missed out, or did configure along the way while tinkering with this device but forgot to mention. So here’s a post about these “open ends”.

  • Previously I mentioned an “ERASE” mode, this is actually “EXCLUDE” mode. This mode should only be used if your thermostat was previously installed in a z-wave network, I guess this was the case when I first set-up my thermostat. The protocol reset does more or less the same but is more extensive. It removes any network information from the HRT4-ZW and returns it to the factory default state (The double press of the dial is to avoid accidental operation)
  • The way incorporate the devices with a controller (in my case the Aeon Labs Z-Stick) is to start with both in an unassigned state. Install each device separately on to your controller. The Association between the two devices may be done using the ‘A’ command on the HRT4-ZW and pressing the install button on the ASR. This does not require knowledge of the node numbers. The install (network) button is required for installation. You need to hold the button down for over a second.
  • I forgot to mention about the wake-up time, I changed the wake-up time while it was in the LI (listen) mode. The default wake-up time is around 23 hours, which is a bit long when you want your thermostat changed. I changed it to 256 seconds or in other words 4 minutes and 16 seconds (the bare minimum value), but I might change it to a higher value again later on.. please see the point below why..
  • The 2 year battery life (as reported by Horstmann) is based on normal use as a stand-alone thermostat. Use in a network where the HRT4-ZW is woken up regularly will reduce this time. That’s why there is a minimum wake-up interval. Battery life should not be a problem in practice, but please note that when the HRT4-ZW is in installer mode (switch 1 up) the Z-Wave module is permanently powered and takes much more power. This is why my battery life reported 90% after some tests. 0% is 2V and 100% is 3V or above. A new set of batteries will normally give just over 3V (2xAAA, 1.5v each)
  • There is actually a second and third configuration parameter I forgot to mention about. The second one allows you to change to Fahrenheit messages. The third one allows you to set a delta t for reporting temperature changes. A message will be sent to associated nodes if the temperature changes by delta t. This parameter defaults to 1°C.
  • When controlled by Z-Wave messages rather than turning the dial, you can actually set the setpoint to 0.1°C steps. This will not show up on the display as it’s only 2 digits, but it will attempt to control to it. For example you could set the setpoint to 20.6°C if you wished. 21°C will be shown on the display as the demand temperature is rounded up. Fahrenheit temperatures are converted internally to the nearest 0.1°C so will not give you more accuracy.

Some really valuable additional information, thanks a lot Mr.Anonymous ! 🙂


Hi, I am Maarten and I am the owner of this weblog. I post on various IT subjects that matter in my life as an IT professional.

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