How to get nest to override the old control

chris day · Jan 28, 2018

after installing the nest and testing the switch return from the heat link to LR terminal the boiler seems to want to only work with the time clock on the front still?

Anyone had similar on a Worcester Combi before

[ElectriciansForums.net] How to get nest to override the old control

Madocks · Jan 28, 2018

Dont they just pull out?

chris day · Jan 28, 2018

Madocks said:
Dont they just pull out?

Hmm it’s ok now, for future reference the time clock needs to remain on with all the pins set to off, I think the LS return overrides

123 · Jan 28, 2018

You would be better to disconnect the Mechanical Timer.

Given the original plastic cover for the boiler most likely isn't there, the redundant timer could be left in place.

Here is the manual for timer.

davesparks · Jan 28, 2018

chris day said:
Hmm it’s ok now, for future reference the time clock needs to remain on with all the pins set to off, I think the LS return overrides

Ls is not the return, it is the outgoing supply to the external controls, which you will surely have used for the nest? Unless you’ve ignored the manufacturers instructions and effectively bypassed the internal fuse in the boiler?

Squid · Jan 28, 2018

Disconnect timer from PCB.

Spunkywads26 · Jan 29, 2018

I have a hive on the same boiler. From memory it was L&N taken from the Ls & Ns terminal in boiler to the hive, link from Ls to common in hive and switched (NO contact) in hive back to Lr in boiler. If you have a time clock or integrated panel set it to permanently on and let the hive/nest control.

shaun1 · Jan 29, 2018

Also, the diagram in post one appears to suggest using a green cable as the live return, which could lead people (who didn't know better) to use a 3 core flex and use the earth as live return. This would not be permitted.