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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3668
Experience:  Heating and Controls engineer
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I have an existing Worchester Bosch Green star 18Ri boiler

Resolved Question:

I have an existing Worchester Bosch Green star 18Ri boiler with a seperate wired room stat. I would like to replace room stat with a Honeywell THR870C Controller what wiring alterations or changes to the existing cables will I need to make- as I like to fit the new room stat/controller unit in the same physical position as at present
Submitted: 3 years ago.
Category: HVAC
Expert:  Andrew Smith replied 3 years ago.

XXXXX XXXXX :

That is fine, try and buy a programmable room thermostat, then you only need a pair of existing cables.

XXXXX XXXXX :

You will need a battery powered thermostat to make this happen

XXXXX XXXXX :

http://www.produktinfo.conrad.com/datenblaetter/550000-574999/560295-an-01-en-THR870CUK_d05.pdf

XXXXX XXXXX :

Looking at the instructions (follow the link above) it will be fine and fit in the existing space with the existing wiring

XXXXX XXXXX :

If there is a neutral at the site of the current thermostat then it will just need isolating safely

Customer:

you mention a " neutral" in your text, are you assuming it is currently wired to a "3 wire" , I not sure..

XXXXX XXXXX :

Yes, a lot of the older ones had a live, neutral and switch wire

XXXXX XXXXX :

You only need to use the live and the switch wire

XXXXX XXXXX :

When these two are connected your heating fires

Customer:

If its a 3 or 2 wire system There is an existing cable system between the existing "Room stat "and the boiler

Customer:

so a 2 core...... I connect to the current Marked terminals, at each end ....and on a 3 wire system keep the live and the "switched live" return lead ...and isolate the Neutral if it has one.

XXXXX XXXXX :

Correct

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