System 2000 Boiler Controller with 2-Wire Honeywell mercury thermostats

I am installing a Tado Smart Wired Thermostat (v3+) with its Internet Bridge.

Here in the US, I have a System 2000 Boiler controller that is controlled by zoned 2-wire Honeywell mercury-switch thermostats each with only a Red and White wire.

I have all the network stuff working but cannot find the right configuration to control the 2 wires so that the thermostat acts as a simple switch (which is all the mercury circuit is).

I have Red into (+) and White into (-) with configuration D01 and without HC and without EK.

What would be better?

Best Answer

  • LonnieV
    Answer ✓

    See my other comment. This particular thermostat arrived without the relay-side contacts, the left side posts for NO NC COM and the other three.

    I realized that I don't need a connector block on both the left and right sides so, lacking the left side block, I popped out the right side one and pushed it into the left side.

    That immediately gave me back access to NO NC COM while trivially removing access to A + -.

    Problem solved.