Change mechanical stat to wireless

[pgtips]

Hi,
There was a wiki on this but it's gone so I need to ask for some help.
I have an old Honeywell mechanical thermostat, 4 wires = earth, yellow switched live, blue neutral and a red live. I want to replace it.
My replacement (dipping my toe in something newer) has a live and neutral input + 2 more ' dry contacts'.
I'm unsure what goes where. Live to live, neutral to neutral but what about earth and yellow switched ?
Thank you

 

[ianmcd]

I have an old Honeywell mechanical thermostat, 4 wires = earth, yellow, blue neutral and a red live.

that is 3 wires not 4, unlikely your new thermostat will need an earth, and dont go by the colours of the wires on a heating system, need to know which new thermostat you want to install

 

[pgtips]

Hi, I have a BHT 002 series WiFi thermostat to install. (Picture attached of old and new)

 

[Deleted member 267285]

L to L
N to N
Yellow switched to 2
Assuming it needs a common link? Unless internal switching?

 

[pgtips]

Assuming it needs a common link? Unless internal switching?

I don't know, I guess I'll find out once I connect it.?

 

[pgtips]

yes, it is missing something. All connected without problem but the boiler is not being switched on when I increase temperature. Is this just the wrong thermostat for the job or is there something else I need to do?
Thanks again

 

[Deleted member 267285]

Did you put a link wire in? What boiler is it?

 

[pgtips]

Hi,
I did not add any wires. It's a Combi boiler, an Atag one.

 

[ianmcd]

Hi,
I did not add any wires. It's a Combi boiler, an Atag one.

which ATAG and what terminals are you using on the ATAG ?

 

[pgtips]

Hi,my atag combi is a A325SEC (X)linked to a Honeywell 7 day programmer, ST9400C. This is linked into my Honeywell thermostat that I was hoping to replace.

I had a boiler and immersion which was upgraded to a combi. So the stat just did temp. One half of my Honeywell programmer is redundant now (the old immersion hot water side I now use it as my autumn and spring program timer for heating)

I know the new wireless stat has its own programs so I assumed I could just leave the Honeywell programmer permanently on and setup the new stat programs.

There isn't a common (C) wire at the stat but I do have 4 wires so potentially have a redundant wire (originally the earth) .

 

[ianmcd]

L to L
N to N
1 & 2 on new stat to 3 & 4 at X5 on boiler, NO links, and you will have to completely disconnect the old programmer

 

[pgtips]

I see it, thank you.
Think it's just jumped to my heating chap when he comes round to service. He wired it originally in the swap to combi so will more competent than me, although I'm not entirely comfortable wiring the combi there must be wires running to the programmer which are already in place.

Thank you for your help though as I understand it a lot more now.

 

[pgtips]

Hi,
I thought I'd follow up my post as I've now got this thermostat installed and working, thanks to my very qualified plumber.

It turned out the stat is actually quite simple, L and N obvious enough but we found when we connected the remaining 2 terminals there was no output, they were dead no matter what the stat read.

A bit more headscratching plumber suggested we try out as though it's a switched live (as it was in the original stat) so we changed wires and fed (linked live) to the switched terminal then connected the original switched live back at the boiler.

And it worked. The programmer is out of the equation completely removed.
Rubbish pic of back of new stat attached, needs tidying now but shows what we did.
Earth is redundant.