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Plumberpro
Plumberpro, Plumber
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Experience:  Heating and plumbing answers. 20 years experience
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Biasi M90E.24S wiring to Nest Thermostat question. Can anybody

Resolved Question:

Biasi M90E.24S wiring to Nest Thermostat question. Can anybody tell me which terminal on the boiler is the "Call-For-Heat" terminal?
Submitted: 2 years ago.
Category: Plumbing
Expert:  Plumberpro replied 2 years ago.
Plumberpro :

Hi , give me a few mins to check the wiring in the manual , thanks

Customer:

sure, no worries.

Plumberpro :

Hi . it will be 3 in metal he boiler wiring block . do you have the manual?

Customer:

okay, so the wall thermostat the I have replaced was wired to pins 1 & 3 and was a simple 'normally open' until it 'called for heat' when the circuit was 'closed' and the boiler kicked in.

Customer:

https://s3.amazonaws.com/support-assets.nest.com/images/tpzimages/Nest-Thermostat-Installation-Guide-UK.pdf

Customer:

in the nest wiring diagram in the link above on page 13, would the biasi common be pin 1?

Customer:

i.e. pin 1 common, and pin 3 'call for heat'?

Plumberpro :

Hi , I will check that link and come back in a few mins. But yes if the nest is a simple in and out then use the same wiring , but just double checking your link

Plumberpro :

Hi , yes 3 from boiler to 2 in heat link nest. , 1 in boiler to 1 in heat link nest

Plumberpro :

Just to put it simply 3 on boiler is common

Customer:

can I just confirm "1 in boiler to 1 in heat link nest"? 1 on the nest heat link is the 'normally closed' relay or "satisfied" terminal. Pin 3 on the nest is 'normally closed' or 'call for heat'

Customer:

sorry... Pin 3 on the nest is 'normally closed' c should have read 'normally open' or 'call for heat'

Plumberpro :

2 and 3 are the connection in the nest.2 is common and 3 is call for heat.according to the manual

Customer:

correct, so should pin 1 in the boiler not be wired to pin 3 'call for heat' on the nest heat link and not pin 1 ?

Customer:


Plumberpro says:

6:39 PM



Hi , yes 3 from boiler to 2 in heat link nest. , 1 in boiler to 1 in heat link nest



Plumberpro :

3 in boiler is common in nest and 1 call for heat . have you tried this ?

Customer:

I can't try it tonight Toby, the installation is at my holiday cottage. I'll be happy to give you a good rating if you can confirm that pin1 on the boiler is 'call for heat' and will connect to pin 3 in the nest which is also labeled 'call for heat' and that pin3 in the boiler is common and will connect to pin 2 on the nest which is labeled common.

Plumberpro :

Ok , just double checking

Plumberpro :

That's correct.

Customer:

cheers Toby.

Plumberpro :

Your welcome

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