Shelly i3 and heating system - no events

I have the following heating circuit. This is single-phase 240V. The relays are thermostats that switch on or off via other means. The motors are 2-way motorized valves that control two water heating zones.Each motorized valve has another cable that goes to the boiler to turn it on or off like a switch. The boiler has also its own Permanent Live cable (this is an S-plan heating system with two zones).

What I wanted to do is put an i3 device to monitor when the termostats request heat, and do plots etc. I dont want to control the circuit, just to monitor the switched live cables. This is the wiring I came up with.

The problem is that it doesnt work.

When I connect the shelly as shown above, the shelly i3 device thinks that the relays are always in ON mode, even when they are off. When the relays get turned ON, the I1 and I2 inputs stay in ON mode - the shelly does not detect any changes in the input. Everything else works fine with the heating system. The event_cnt counter stays the same no matter how many times the motors get turned on or off.

I have measured the voltage between the two sides of the relays (i3 L vs I1 for example) and there is 245V when the relay is OFF and 0V when the relay is ON. So I am not sure what is the problem here.

I saw some mentions in this forum that this setup may require coupling relays, but not sure I understood why. Another solution would be to use a Shelly EM I suppose, with two clamps, one for each switched live. It seems like an overkill though, I do not want to measure the power (this is a gas boiler, it does not draw much electricity, the whole circuit has a 3A fuse).

Any thoughts on that? cc @Olsche  @Guzzi Charlie

Zitat von thgoebel

If you are skilled in electronics (or you may a have a friend with this profession), you should add two resistors:

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Resistance is not critical: 470kΩ to 1MΩ will work. Each resistor should bear 1W - this is more than tripple oversized. For a secure implementation look at this thread: click (unfortunately in German language). If you should have any question in the implementation or in sourcing the parts, you may send me a PM!

Oh thats very interesting! I'll read the linked thread via google translate.

So the i3 needs some small load in-line to understand the status of the switch?

I thought the voltage differential between L and I1/I2 would be enough. I'll definitely try that.

I tried reversing the inputs, there is no change. The shelly inputs gets stuck to OFF (instead of ON), no matter what the real relay status is.

No events are counted when switching, still.