Nest V3 Opentherm and ideal vogue S32 gen 2 Shambolic help ??

[Matthew Darch]

Hello , so I recently completed a self build house , we've been in now for 6 months and its great , a few teething problems here and there , hence my post;

So the plumber has done a great job its a medium sized 4 bed and has a Vogue S32 Gen 2 boiler with radiators throughout .
The plumber advised having separate Zones upstairs and down so thats how its plumbed.
I bought 2 nest V3 originally intending to have 1 upstairs and 1 down , with the downstairs one doing hot water.
I then read up about opentherm and thought it sounded the way to go , the plumber hadn't heard of it so he was as much in the know as me, after much research it was thought that opentherm would only work with one nest so the separate valves for upstairs and downstairs were wired together to create one zone.
I must admit the wiring diagrams were not very clear , saying to just wire the two opentherm wires which we did but things didn't work properly.
In the end it got wired with a combination of opentherm and the normal wiring and it worked so we just went with it .
Anyway im not convinced its wired right , I suppose my questions are ;

1 which would you think would be more efficient set up , a single zone opentherm enabled system or a dual zoned traditional wired system ?

2 has anyone got a dual zone Nest system working with open therm ?

3 for those that have had a nest system working with opentherm , should I see the flow temps on the nest ? as I do not presently.

Any ideas or tips for the wiring ? id get the plumber back to do that so it's covered.

Thanks in advance

 

[Dan Robinson]

has anyone got a dual zone Nest system working with open therm

I didn't pick up on this in your message.

You can't have two OpenTherm Nests on one boiler - unless is it an Intergas X series. At best the first Nest to power up will declare itself the master and the other one will be ignored or just send the boiler to max flow temp.

The easiest way to get what you require is a dual zone Honeywell T6 set up which will aggregate demand to the highest load, or Evohome which will do the same down to room level.

@shambolic will confirm other queries hopefully. Or if you are super lucky our resident teaboy and general knownothingatall @hard-work will pipe up with his vast [sic] knowledge

Sorry, it's been a long day.

 

[hard-work]

Not bad Dannyboy. Not bad. You are getting there. Don't go down the computer network techie road as that is not your fields for sure.

 

[bernardgreen]

To be fair to installers of heating system the OpenTherm system today is a bit of a hash up and difficult to understand.

The original 1995 "concept" was a fit all solution for one thermostat to connect to one boiler. But since then it has been added to and tweaked to make it even more flexible to enable one design of hardware to cope with :-

(1) simple mechanical thermostats with ON_OFF control ( short the wires together with the switch in the thermostat and the boiler must fire up )

(2) intelligent thermostats that control the temperature settings and other parameters in the boiler

and many variations of controllers between these.

In terms of control the thermostat is the Master and the boiler is the Slave. That is fine when there is only one device that has to be Master to the boiler ( the Slave ).

When there are more than one device that has to control the boiler then the original concept is no longer viable. One Slave to many Masters, difficult to manage if the Masters cannot communicate with each other and agree on what their one Slave has to do.

Any system with one Slave ( the boiler ) and several Masters ( thermostats and othe types of controllers ) requires a means to decide the order of priority that the Masters have when they have conflicting requirements for the Slave to carry out.

Enter the Gateway (*) a module which allows more than one Master to control the Slave by assigning a level of priority to each Master, ( at least that is how it was explained to me ).

At this point the electronics hardware and communication protocols have become complicated and the simple 1995 concept has been lost.

(*) other designs are available with different names.

Some will no doubt say this is a post full of waffle. They are welcome to their opinion given that their training on OpenThem may not be all encompasing.

 

[hard-work]

Bernard, you are right the original simple OpenTherm concept has been lost. A gateway can be on a pcb, the software to control the it all on the pcb. But it can still be just a simple plug and play using any makers OpenTherm compatible device. The ignorance surrounding it is amazing, as Matthew stated, his plumber had never heard of it after all this time. How many OpenTherm compatible boilers have a crude on-off stat on it, when an OpenTherm stat would greatly improve matters all around. The Intergas X range has dual OpenTherm terminals as Dannyboy says.

The Intergas pcb is not that smart as it cannot have the outside temp sensor and the OpenTherm room stat working together, it's one or the other, with room taking precedence I believe.

 

[Dan Robinson]

The Intergas pcb is not that smart as it cannot have the outside temp sensor and the OpenTherm room stat working together, it's one or the other

Oh dear.

 

[hard-work]

According to the manual that is the case Dannyboy.

8.7 Weather-dependent control
When an outdoor sensor is connected, the flow temperature will be automatically controlled according to the set heating line, depending on the outside temperature. The weather-dependent control functions solely with an on/off room thermostat. When using an OpenTherm room thermostat, the outside temperature will be relayed, but the heating line of the central heating boiler will not be active.​

So, the OpenTherm stat is given control of the burner's modulation rendering the weather compensation redundant.

 

[Dan Robinson]

So what happens when a pair of T4M's are fitted

 

[hard-work]

Dannyboy. I cut and pasted from the manual just for you. I never made it up.

 

[Dan Robinson]

So what happens when a pair of T4M's are fitted

 

[bernardgreen]

So what happens when a pair of T4M's are fitted

Can two T4Ms be connected to a single boiler ?

Two masters ( T4Ms ) and one slave ( boiler ) ! How are priority levels assigned to the Masters ?

 

[Dan Robinson]

The x series Intergas can accept two OpenTherm thermostats

 

[bernardgreen]

The x series Intergas can accept two OpenTherm thermostats

More details please, assuming that is you have more information than just the advertising gunff.

I repeat the question How are priority levels assigned to the Masters ? ( in other words which thermostat has priority )

Or does the x series have two separate heating zones each with its own Master-Slave OpenTherm set up. The two zones then share the one boiler.

 

[bernardgreen]

With a bit of research I think I have found the answer

I have under lined the important part of this quote frorn Version 2 of the OpenTherm specification

2.1 System Architecture and Application Overview

OpenTherm is a point-to-point communication system and connects boilers with room controllers, therefore it is not possible to connect several boilers or room controllers
in the manner of bus-based systems.

OpenTherm assumes that the room controller is calculating a heating demand signal in the form of a water temperature Control Setpoint based on room temperature error (or other control form, e.g. OTC) which it needs to transmit to the boiler so that the it can control the output of the boiler. The boiler in turn can transmit fault and system information to the room controller for display or diagnostics. A large number of data items are defined in the OT/+ Application Layer Protocol, covering these and many other pieces of system data.

2.2 Provision for Future Architectures/Expansion

In order to address applications which would normally require a bus-based communications system, it is conceived that intermediate gateways / interface devices
would manage multiple OpenTherm communications lines. In the example below, the interface device acts as a “virtual boiler” to the room controller and acts as a “virtual room unit” to the boiler. In this way, other devices can be addressed while maintaining the basic point-to-point approach.

I assume the blue box has been built into the Intergas Series X boilers.

 

[hard-work]

Because OpenTherm is not a 'bus' based system, it put many makers off it, like Vaillant. There are ways around it but it requires come clever stuff on the pcb, which raises the price of the pcb and hence boiler. Replacement pcb's on the basic Intergas boilers were £400-450 the last time I looked with that not having any interface device on the pcb or the likes of.

When most plumbers only put in simple stat/timers on combis, as that is all they understand, many makers will not go that far to keep the price of the boiler and spare parts low to increase sales, or keep sales figures stable.