room thermostat for Worcester Ri 18kW, existing dial switches 240V, seems dry is the norm?

[Bignose2]

Hi,

Recently had a new Worcester Ri 18kW installed.

Wan to change the room thermostat, just one zone.

Left existing honewell dial but would like to change for a digital & ideally WiFi
Ordered one from Amazon, says for Boiler but on reading the instructions it uses a dry contact, no 240v switching.

Fairly sure I am understanding the old wiring. As original connections
(1) Live source
(2) N
(3) Switched L (240v) when I turn the stat temp up, zero volts when turned down.
Earth far left, (4) Not connected.

Appreciate the new one below is wrong, did test & never does it put 240v onto any of the other terminal.
Would not have thought too much of this but reading online says most use dry contact & I think even specifically the Ri 18kW.

a) Is this 240v switching fairly normal & just wired differently at the terminal box at the boiler end.
b) If I got GB, should that work switching live. I only have one N into the control, can I share that, may not sue that anyway back at the boiler but perhaps the thermostat won't be happy unless it has a N on (3) also.

I read elsewhere that live is passed through the thermostat & the switch causes the "break" indicating teh call for heat. Describled as nto the same as 240v switching but don't see the difference.

I had some similar'ish stats I put in Daughters house for electric underfoor heating btu that was very straight forward & of course put the 240v direct to the heating. They were for "underfloor" so had the correct internals from the off.

Many thanks in advance for any advise.

 

[ShaunCorbs]

That’s a weird instructions book

Looks like there switching neutrals which won’t work for yours

You want version ge

 

[Bignose2]

Thanks for you reply,

Not quite sure how GE would work.

As I say my old dial switches 240v which assume I need to replicate

Just checked again testing from earth, the old Honeywell ..
(1) Live source, 240v
(2) N
(3) 240v when I turn the stat temp up, zero volts when turned down, in my case grey wire.
Earth far left, (4) Not connected.

N0 & N1 surely are just Neutral, I need 240v to go down the signal wire.

 

[RBG]

What is the make / model of your new thermostat?

 

[ShaunCorbs]

Thanks for you reply,

Not quite sure how GE would work.

As I say my old dial switches 240v which assume I need to replicate

Just checked again testing from earth, the old Honeywell ..
(1) Live source, 240v
(2) N
(3) 240v when I turn the stat temp up, zero volts when turned down, in my case grey wire.
Earth far left, (4) Not connected.

N0 & N1 surely are just Neutral, I need 240v to go down the signal wire.

Your switching live

Gc switches neutral

For ge

Perm live to live 1
Neutral to neutral 2
Switch to no4

 

[Bignose2]

Many thanks

So the NO terminal will feed the 240v (from L terminal 1) to the boiler when stats turned up?
guessing to the 2 port valve (there are two separate 2 port valves, HW & CH)

I was thinking a Normally Open terminal was just closing a circuit without voltage so as to signal the bolier.

The old Honeywell T40 really just shows & describes as switch live, nothing about NO or NC.

 

[ShaunCorbs]

Many thanks

So the NO terminal will feed the 240v (from L terminal 1) to the boiler when stats turned up?
guessing to the 2 port valve (there are two separate 2 port valves, HW & CH)

I was thinking a Normally Open terminal was just closing a circuit without voltage so as to signal the bolier.

The old Honeywell T40 really just shows & describes as switch live, nothing about NO or NC.

In theory yes

And yes but there no common terminal so there has to be a link inside you can test put live and neutral to the stat

Turn stat on eg you want heating / call you should get 240v on one of the terminals (with a multimeter) and turn the stat off eg you don’t want heating / call this should remove it