Wyze Thermostat C-Wire Requirements Question

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Thermostat Controller Upgrade: Chronotherm IV to Wyze

We currently have a Braemar TA20n Gas Ducted Heater and a Honeywell T8602D Chronotherm IV thermostat controller. We want to upgrade to a Wyze smart thermostat and understand we need a C wire connection to provide power. I have read the Wyze thermostat simplified block diagrams guidance and other C-wire posts which were very helpful, however still have a query specific to our installation that I was hoping could get some advice!

Our current 2-core wiring only has the R and W wires connected as shown in Figure 1 and 2.

While the ducted heating control board indicates it does have a C terminal, the wiring diagram shown in Figure 3 only indicates the W and R terminals.

We have an Olex 3 Core 0.75mm electrical cable with stranding 24/0.20mm wires, shown in Figure 4, that we were planning on replacing the current 2 core cable.

Before proceeding, was hoping to see if anyone had answers to the following queries…

  1. Without a multi-meter, is there a way to tell whether the heating control board C terminal is powered before I change the current 2 core cable for the 3 core cable?
  2. Is the 3 Core 0.75mm stranded wire electrical cable appropriate for the Wyze smart thermostat? I saw some smart thermostats indicated they weren’t compatible with stranded wire cables?

Thanks in advance for any help!

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Stranded wire is fine.
Your C terminal should be connected to the transformer and earth,
The easiest way to find out if it is going to work without a multimeter is to connect something that needs 24vac to turn on to the R and C terminals - if you already have a wyze thermostat, try connecting it temporarily and see if it powers up before running new thermostat wire.

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Thanks, very helpful and good to know stranded wire is fine. Don’t have Wyze thermostat yet as wanted to test before purchasing. And haven’t been able to find another 24 VAC device about the house to test. Will see if I can borrow a multimeter from work or a friend.

There actually was another wiring diagram on the inside of the ducted heating unit lid, however while this does indicate the ‘C’ terminal in the terminal block it is still not clear whether it is connected to the transformer and earth.

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Thanks again!

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C means common, it is pretty much always the return path for the 24v hot when dealing with thermostats.