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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3646
Experience:  Heating and Controls engineer
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Hi I have a Worcester Bosch Greenstar 24i Junior boiler about

Customer Question

Hi I have a Worcester Bosch Greenstar 24i Junior boiler about 5 years old. It has a DT10 controller fitted and I have a wireless thermostat. I have purchased a Nest thermostat which has an external controller. So I need to disable the DT10 and wire in the new controller. I know I need to connect to the Lr and Ls terminals but how to disable the DT10 in a state where it is always on (presumably)
Submitted: 3 years ago.
Category: HVAC
Expert:  Andrew Smith replied 3 years ago.

Andrew Smith :

Does your version of the DT10 control the heating and hot water?

Andrew Smith :

It is possible by leaving the other controller on continuos (24 hours) and then connecting the new stat to the boiler

Andrew Smith :

All controls wired in series - in out, in out, in out like a Christmas tree

Andrew Smith :

That was if any turn off then the circuit breaks and the boiler truns off

Andrew Smith :

So the receiver will take the mains and two cables from Ls and Lr - you could use a single 4 or 5 core cable

JACUSTOMER-xcaq5k2i- :

Hello Andrew,

JACUSTOMER-xcaq5k2i- :

Hello Andrew. I am partially familiar with the Greenstar 24i so I already knew I had to connect to Lr and Ls terminals. But just connecting an external controller was not sufficient. but what I needed to do (hence the question) was to disable the existing controller. Well I found the answer here https://community.nest.com/message/27953#27953 all that is need is to disconnect the ribbon cable from the DT10. So it is important not to leave the existing controller in the system (even on 24 hours would not work as it is still controlled by the old wireless stat) Tony

Andrew Smith : It would still work with the clock connected, as I have done this before
JACUSTOMER-xcaq5k2i- : Hi Andrew thanks but if you have the internal controller connected it only works if the wireless thermostat is set to always on. This is not a practicable solution why would you do that? And it consumes battery power from the wireless thermostat. Far better to remove it from the system.