Help! Nest - Dual zone - Opentherm!

[1animal1]

Afternoon all

After getting to a point where i am almost ready for my new boiler system to be fitted. I am going for either a Viessmann or unvented but i think swaying towards the unvented due to hot water contingency if the boiler goes down (too many stories of people waiting days for parts, taking cold showers!). I have rigged the system to be easily converted to two zones for CH, S plan (currently one loop, S plan), obvious hot water and possibly a single water underfloor being added eventually.

My original intention was to go with NEST gen 3 x2, one for each zone and the lower zone controlling the hot water. This is a medium sized 4 bed detached property, so nothing worryingly huge.

Yesterday i took the time to contact a really helpful chap enquiring about Evo Home which I can see is a far superior system, especially when linked to Opentherm! My problem is the usual cost associated given that I have 11 rads, 2 of which (designer) have nice shiny new valves which won't be Evo compatible and are quite prominent (kitchen/Hall).

This got me thinking about the benefits of Opentherm and upon reading, it sounds daft to ignore it. My problem is this though - from what i understand you cannot have duel NESTS on Opentherm as it understandably can only be controlled from one source, so is my only solution to stay with one ring? Maintaining what is in place now..... if i want to use Opentherm....

Possibly going to a single ring on Honeywell connect, using Opentherm bridge, hot water bridge - meaning i'll be opentherm from day one and able to add the TRV therms once i am able to afford (might need a second job just to pay for 11 of those :/)

 

[robj20]

Yes.
Thermostat wise you have the choice of the classic looking one and the round digital display one which I much prefer the look of.

 

[1animal1]

The round one does look a lot better - although I would hope they are looking at a colour screen eventually, it looks a tad dated

So the Opentherm link connects to the boiler and sited next to, the hot water sits with the cylinder - and everything talks to the communicator...simple as that?

I called Honeywell earlier and they couldn't get their head around the zone stat working without an actuator - saying that the communicator will always ask for both.

 

[robj20]

Pretty sure you can for instance have evohome with nothing but the controller and it just acts like any other system.
I can't remember if it requires an actuator of some sort as well when binding the thermostat.

Where are you buying from. Evohome shop were very helpful when I needed help.
Just need to know if you can bind just a thermostat on its own to call for heat.

"Zone Temperature Sensing, Sensor Control for HR92 Radiator Controllers, Control of Single Zone Valve Operated Zones, Kickspace Heater Control, Single Zone Underfloor Heating Control and much more!"

The first one is what you would be using it for. I use it for the third one. Probably use one for a kickspace heater when I do up the kitchen as well.

 

[1animal1]

I have spoken to Richard at Evohome, he's the one that made me consider this initially.

I may well go to them for a package price, however nobody seems to want to shift on cost and the overall is over £150 more expensive with them... but then weigh up the cost of not buying something from a reputable firm who know what they are doing.

I can get the 3100 cheaper at the moment so i will have the relay spare if not required for the zone stat. That's an option... Easily tested with the controller and stat on my lap I imagine, like when you bind the TRV's?

It can get very complicated and a possibly a little addictive this smart tech

 

[robj20]

Yes you could test them. The controller has a page which shows what's connected which is very handy.

 

[1animal1]

Thanks Rob - A huge thank you for your help with this.

 

[1animal1]

I've had quite a result with this - Plumb Centre, 20% off the first order (max £100)- despite them having various packs, the best value was the Evo connected, hot water and 4 TRV's and a separate 4x TRV pack. All that for £557.... I'm sure trade is less (I've a sparky mate checking that with his main account) - I can always return if a better deal appears....

Just Wall mount, remote stat and Opentherm bridge to source - managed to get a single HR92 from Wolseley Clearance for £41 too... not bad for an hours bargain hunting

 

[1animal1]

Rob, just trying to get my understanding correct. If connecting the opentherm, do I still connect the BDR91 to the boilers other terminals and 2 way valve?

I've also had to reconsider the thermostat for the bathrooms and buy two extra trvs. Whilst the stat could call for heat, the rads would also heat up when any evo trv requested heat... So I could either fit a 2 way valve having to convert the 15mm to 22mm or suck it up and make do with a digital trv in each bathroom... I have gone for the latter

 

[robj20]

Rob, just trying to get my understanding correct. If connecting the opentherm, do I still connect the BDR91 to the boilers other terminals and 2 way valve?

I've also had to reconsider the thermostat for the bathrooms and buy two extra trvs. Whilst the stat could call for heat, the rads would also heat up when any evo trv requested heat... So I could either fit a 2 way valve having to convert the 15mm to 22mm or suck it up and make do with a digital trv in each bathroom... I have gone for the latter

No the Opentherm is instead of the bdr91.

 

[1animal1]

Bloody hell mate, wasn't expecting a reply this late

So I can get rid of the BDR that came with the controller and the other that comes with the hot water kit

 

[robj20]

Bloody hell mate, wasn't expecting a reply this late

So I can get rid of the BDR that came with the controller and the other that comes with the hot water kit

I have no experience of the hot water kit, so can't help with that.

 

[1animal1]

The instructions talk about the hot water stat binding to the controller first, then binding the BDR91 which will be the control.

I imagine the opentherm bridge will open up control to the boiler to the communicator... As otherwise the boiler would be wired both ways.

Can anyone confirm?

 

[robj20]

I would imagine you would bind the cylinder stat then a bdr91 which will go on a diverter valve of some description.
This would then switch the valve via the bdr91 and fire up the boiler via the Opentherm Bridge.

 

[1animal1]

Good point... The wiring diagram points to the boiler and 2 way going to a junction box, so didn't know if the boiler would have any control over the 2 way what so ever.

That does make sense though and explains why there's a separate wiring spec just for a 2 way...

 

[1animal1]

So... where I am with this. I am going to be wiring the system to my Y plan circuit this weekend - to get it up and running and learning - it also means a partial disabling once the opentherm system goes in, so less work to do later.

My question is this though - I can see in the instructions that it can be applied to a Y plan system with no HR92's - i can also see an ideal Honeywell circuit with a 2 way valve for the HW and nothing on the CH piping, whilst using HR92's (which aren't on the Y plan diagram).

I presume given the wiring of the 3 way diverter goes into the boiler and HW relays - that when binded, the commuinicator will take signal from any of the HR92's and then switch the boiler on and point the 3 way in the right direction... but I don't want to disable everything before finding that out.

My pump and 3 way is currently upstairs in the middle of the house, the boiler and stat are downstairs - so i am pretty much going have to go back to basics, setting a new junction box in both locations - utilising the existing embedded wiring joining both locations - so it won't be simple putting it back together once stripped

Thanks in advance

 

[gpbeck]

Don't forget to always leave all the internal doors closed...

 

[robj20]

Don't forget to always leave all the internal doors closed...

I have found I haven't needed to. For instance dining room and living room are open, right now I only have the heating on in the living room which shows 20c and the dining room is 17.5c.

 

[gpbeck]

I have found I haven't needed to. For instance dining room and living room are open, right now I only have the heating on in the living room which shows 20c and the dining room is 17.5c.

It's only September.

 

[robj20]

It's only September.

It is indeed. I have most rooms set to either 17c or 19c. If it goes colder the heating comes on.

 

[gpbeck]

Suspect warmer air is wafting out of your living room and upstairs, just like mine!

If you close the door, won't the flow temp fall?

 

[1animal1]

Update! I'm fully wired up and the system is working. So far it's only been a day but I am highly impressed. Just need to refine the schedule to suit our comings and goings.

I have replaced one of the heads for our en suite with a manual one for now as I don't have a relief valve fitted... Set this at 2 out of 5, so hopefully that will protect it until the new system goes in.

Thanks for everyone's help on this, notably Rob and Shaun... Thanks chaps

 

[robj20]

It soon learns the rooms, at first mine all overshot the temps, now it knows when to switch off to hit the target. For the living room set to go off at 20:00 it is turning off around 19:00 now.
When it has the rooms up to temp the boiler is still cycling a bit but the flow is only around 32c.
Maybe when the whole house is falling for heat it will not cycle at all.

 

[1animal1]

That's interesting... Is it possible given the age of my boiler that it won't have the capability beyond on and off? It is 31 years old

Have you got both optimize options set I gather? I've set the start up option for 1 hour prior

 

[robj20]

No I just have the off one set.
Didn't you fit Opentherm?

 

[1animal1]

Not yet.... That's on the new system which will be fitted at the start of next year. I've a few jobs to do yet... Including sorting the electrics, clearing space and shifting things for the new cylinder etc...

This is the original 1986 boiler and open vented cylinder. Not doing bad considering