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PostPosted: Thu Apr 27, 2017 9:05 pm 
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Hello all. I'm moving house soon and want to take my Nest thermostat with me. It was installed for free by Nest as part of the launch promotion.

Let me preface this quickly: I'm competent with electronics and circuit troubleshooting, but boilers are new for me. I know how to stay safe around mains voltage.

The Nest Heat Link (thermostat receiver) power is spliced in to the boilers mains supply on the mains connector block. This is easy enough to disconnect. The thing I'm less sure about is how the Heat Link relay wires were wired in to replace the old built-in mechanical timer module which now sits unconnected in the boiler. I want to restore functionality of this timer while removing the Nest. The boiler is a Baxi 105e.

Here are some photos I've taken of the boiler wiring:

This picture shows the mains connector on the left and Heat Link wiring. White multi-core cable in upper left is connected to the HL and will be removed. Black and grey wires coming from this are the HL relay wires.
Circles indicate wire connections. Red connects one HL relay wire to the front panel power/mode switch. Yellow connects other HL relay wire to PCB connector.

Here's the unused mechanical timer module. Green circle shows two wires shorted together. There are two unconnected spade terminals on the module. These are the timer switch connectors. Connected wires are mains power.

The two shorted wires in the above picture go to this connector on the main PCB.

The installing engineer left these parts inside the boiler for safe keeping. I recognise the two spade connectors as coming from the timer module, cut off from the two wires now shorted together. The yellow jumper I don't recognise.
I understand that the spade connectors will need to be re-attached to the two shorted wires and connected back to the empty spades on the timer module.

The questions I have are:
  1. How are the remaining red and yellow circled wires, in the photos linked above, connected to regain the old timer control? Am I correct in thinking I just need to connect them together using the connector block?
  2. Where does the yellow jumper go?

Many thanks to anyone who can help me out here. :-)

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