Install of nest 3rd gen

this is what we have at the moment.

in the utility room we have

• a ferrolli boiler
• a siemens rwb27 controller

up stairs

• there is a seperate on off switch for an immersion which provides hot water only

but when the siemens is switched on, it heats the house and also heats the water
the switch upstairs is for water only

we do not appear to have a thermostat, our heating is manual, and turned on/off by us or by a timer system.

i have attempted to install the nest, i have made the error of thinking it would be simpler than it is..

https://imgur.com/a/ljaaKsI
https://imgur.com/a/xTlzyPA
https://imgur.com/a/JGaO07W

As you can see, there is a L & N
the L is looped through to 2, to enable 240v system
there is a second wire connected to the 2 ( aside from the loop from L )
there are 2 wires in the 4 position, one is brown and one is black

my understanding is that the 2 position is call for heat off
and the 4 is call for heat on .

but.
if you look at the nest diagrams, they use different terms

https://imgur.com/a/0zkWfng

so
can someone help me with the following.

the wiring for the nest
can someone explain the ch off ch on thing.
is call for heat off - an open system ( an open circuit)
is call for heat on - a closed circuit, thus engaging the boiler

the two wires in the 4 position, is one of them a controlling wire for the immersion system, would it be possible to wire this into a different position in the nest, so that we could control our hot water from the app
if so, would it be a case of identifying the cicuit for the boiler i.e ch on ch off , and then the remaining wire must be for the immersion.

thank you

this is how I wired mine.... this pic doesnt have the live and neutral added yet which I put in blocks as there was a few of them and the nest controller can only fit 1 cable in.....

thanks for your help but i dont understand parts of your setup
how come you dont have a L or N attached?

in case someone wants to get involved
this is a diagram of my previous setup using the siemens rwb27

4 - Bl wire, #2 wire
3 -
2 - #1 wire, looped through to L
1 -
L - L along with wire to position 2
N - n wire

so my understanding is that

4 - Ch On, Normally open , call for heat
3 -
2 - Ch Off, Normally Closed, Satisfied
1 -
L
N

so in order to wire the nest heat link correctly

3- #2 wire, Bl Wire
2-
1- #1 wire and connection to L
L- L wire + connection to position 1
N- N wire

is that correct?

thank you

Your post is a bit confusing. You show a photo of an RWB 27 timeswitch which seems to be existing, a photo of the wiring connections to a Hive Dual Channel receiver, and also photo of the wiring connections to a Nest Heat link!

The RWB 27 is a simple timeswitch it provides one channel simple on/off time control as shown in the diagram you posted.



It doesn't have two channels one for heating and one for hot water like either the 'Hive' or 'Nest' photos you posted, both of which are dual channel.

Hive.


Nest.


So you are not exchanging like for like, they are different items with different functions.

From what you post, something sounds wrong here. The same timer seems to control the boiler's heating of the radiators and also the hot water. If so, the system will probably require rewiring to provide separate timed control of the hot water and central heating.

BTW, an immersion heater is a separate electric heating element that is inserted into the hot water cylinder to heat the water electrically. It has nothing to do with the boiler or its controls. A similar scenario would be that if you had central heating that heated a radiator in the living room, but also had an electric heater in the living room. Both would heat the same room, but are no way connected to each other. In the same way the boiler and immersion heat the same hot water but are not connected to each other in any way.

sorry, i made a mistake with the HIVE diagram.
so ignoring that diagram
is the position 4 on the siemens a call for heat with position 2 being live out?
there were 2 wires on #4 , a black and a brown
there was 1 wire on #2 a brown

so its not possible that one of the wires on #4 was something to do with heating the water?

i have rigged up the nest now, i dont think its 100% but it is semi functional when i use the manual heating button

the way i rigged was
on the nest
neutral - neutral wire

live - with a connection to #2 and then onto #5
i put the brown wire on #3 and the black on #6
and then the live out cable is in #5 too.

so now the heating and water heating work when i press the manual button on the heat link
but, the thermostat itself doesnt seem to have an affect.

The RWB 27 timeswitch has a single switch between contacts 2 and 4, when the switch is 'on' they are electrically connected. But it is a single channel timeswitch. Terminal (2) is the live supply and (4) will go out to the heating and also the hot water (if they both come on together)

So, it appears that this single timeswitch is controlling both the heating and hot water. The reason you don't have a room thermostat now is probably because the way it is wired up would mean that a room thermostat would also turn off the hot water also.

Nest is a two channel timeswitch, one channel for heating, plus one channel for hot water.

You cannot replace the RWB 27 as it stands with the Nest. It will not work. They are different things. There are not enough wires present at the RWB 27 for separate control of the heating and hot water. The system will need rewiring. What this involves would depend on the type of heating system you have. But you don't give any information about this.

Just be careful, if you keep swapping wires around in this ad hoc way without understanding what each wire actually does and what you are connecting it to, you run the risk damaging the Heat link.

okay, honestly, thank you very much for your help. im going to get an electrician out this week to complete it.
thanks again

I am reading between the lines, so I may be completely wrong? I am guessing that your system is like my dads old system, with the domestic hot water being heated with a hot coil in cylinder and an immersion heater? The hot coil either thermo syphon or piped like a a radiator, if so you have no control of domestic hot water, it simply gets hot when central heating is running.

What I realised with dad's system, it was really back ground heating, it got house warm in morning, and early evening before fire was lit, however to use without lighting fires, it needed some way to turn off boiler, if it was left on, it would cycle off/on all day, as it continued to try and heat the domestic hot water.

The cure was to add a motorised valve, this was connected to the cistern thermostat in our case wifi linked, this turned the motorised valve open/closed which in turn turned boiler on/off. So from this point the central heating could run all day, however in dad's case, then the header tank started to leak, so he replaced the lot with a combi condensing boiler.

Your first move is to work out what you have, then decide how much you are prepared to spend, fitting all new parts to improve is only any good if they are going to last, and if your using thermo syphon then the system is rather old, and not that economical.