Wiring help needed!


I've been struggling to wire up Tado extension kit as they don't have my Time Guard FST77 on the installation guide.

Anyone out there who can help me? Tado haven't been very helpful so far and I'm desperate to get the system installed and running. Attached are the photos. (Sorry about the angle of the pics- I've explained what's going on in them below).

We have 6 wires:

Left top (red) L IN

Left bottom (red) L OUT

Right top (black) N IN

Right bottom (black) N OUT

2x Middle bottom (green and yellow) T40 

I'd like to thank anyone in advance for their time!

Kind regards,



  • Hi Chloe,

    The Time Guard FST77 is a fused spur timeswitch, it is probably just controlling electric immersion heated hot water.

    I’m pretty sure Tado only works with Gas fired boilers for heating and hot water heated via a coil in the water storage cylinder which has hot water from the boiler passing through it from the boiler.

    Do you have a central heating system and a separate controller for that?



  • Hi,

    As Sean has pointed out, this timer is often used for an electric immersion heater, and therefore there is a high likelihood that too much current is switched for the Smart Thermostat to handle.

    If you haven't done so, we strongly urge you to contact our support for help with the installation: https://support-request.tado.com/#/contact?locale=en

    Best regards,


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