Ok so I'm working on a thermostat project at the moment got a question around the switching. The boiler that is fitted in the house is a Maxi Duo-Tec 20 HE and uses line voltage for the thermostat.
Was looking at using and opto-coupled relay: http://www.ebay.co.uk/itm/151835137152
But I'm not sure how boilers work and given it's 230v 
don't want to be making mistakes.
Any guidance would be awesome 
Sorry forgot to attach the thermostat stuff that's in the boiler install guide
You need to explain exactly what you want to do with the Arduino.
...R
Basically turn the boiler on and off via it's thermostat control, I've done all the arduino side programming etc
Is it just a case of putting the relay NO connection across pins 1 and 2 or is there something else that needs connecting etc lol
I thought you had a more complex problem involving reading the thermostat etc.
As far as I can see you just need a relay across bk1 and bk2.
I have no idea whether the closed position of the relay signifies "turn the boiler on" or "turn the boiler off".
...R
Why is there a neutral going to the thermostat? Is there more to it than a simple pair of contacts?
Weedpharma
I believe the boiler is a Baxi (not Maxi). The manual is here http://www.baxi.co.uk/documents/duo-tec-he-a-installation-instructions.pdf
The thermostat information is on page 34. There are two diagrams of the thermostat circuit. and the following note
NOTE: The 230V switched signal for external controls
(Frost Stat - Room Stat - Timer) must always be taken
from terminal 2 at the boiler. Live, Neutral and Earth to
power these controls must be taken from the Fused Spur.
I believe that the thermostat as shown maybe powered using the neutral and one leg, or it may be related to the anticipator heater.
Replacing the thermostat as shown with an arduino controlled relay should be to just close the circuit between 1 and 2.
The relay as shown in the original post is 12v. How are you powering it?
weedpharma:
Why is there a neutral going to the thermostat? Is there more to it than a simple pair of contacts?Weedpharma
That's what threw me on it lol
cattledog:
The relay as shown in the original post is 12v. How are you powering it?
By opening my eyes and reading it would seem lol ooppss
I've got a 5V power supply to feed the arduino and relay with a 3.3v step down to power the nrf24l01.
Now to get one of these instead: http://www.ebay.co.uk/itm/161846583843
my bad
Thanks for your help guys it's much appreciated.
Now to get one of these instead: http://www.ebay.co.uk/itm/161846583843
That link does not work.
Would this be suitable?
PaulRB:
That link does not work.Would this be suitable?
Strange works for me 
It's basically the same as in the first post but a 5v version. Didn't even think to look at a solid state relay tbh.
SteveSin:
Strange works for me
Yes I can see it now on my laptop, couldn't earlier on my phone.
Don't think there is much advantage to a solid state relay. They are quiet and don't wear out, but for you application, that probably doesn't matter much.
Slightly strange seller: rat poison & Arduinos! No worse than all those Chinese "bazaar" sellers I suppose.
Some of their items say
When we say UK stock we mean you can come and collect it!! Many sellers out there saying UK stock // Seller ??????????????? I don't think so (read the contact seller (bottom left hand side of page) How many sellers are there in Portsmouth Shenzhen? )
But then they leave stuff like this in the product description:
The interface design of human nature, all interfaces are available through a direct connection terminal leads, very convenient
I'm just nit-picking, they are selling the same stuff as the Chinese sellers, and the price is OK for a UK-based seller.
PaulRB:
Don't think there is much advantage to a solid state relay. They are quiet and don't wear out, but for you application, that probably doesn't matter much.
Yeah it's going to be locked away in the cupboard where the boiler is so noise isn't really any issue, plus I've got a piezzo buzzer on the main unit to notify when they heating turns on.
haha yeah it's pretty hard to tell who are genuine UK sellers, I love how they mention Portsmouth given that's their location.
Think the chinese sellers use Portsmouth cause that's where the shipping containers with all the goods they've shipped over are stored, so they just go and get what they need as and when it's sold on ebay lol.
SteveSin:
Think the chinese sellers use Portsmouth cause that's where the shipping containers with all the goods they've shipped over are stored, so they just go and get what they need as and when it's sold on ebay lol.
I think most of it is in bond so they only have to pay duty when its shipped.