Nest Thermostat (with Open Therm) on Worcester Bosch

[Mark72]

Hi
I have a Worcester 30i combi boiler which had a Worcester Wave thermostat fitted, which is now longer supported

So I decided to replace it with a Nest 3 generation thermostat. The default setup with Nest and Worcester Bosch seems to be On / Off temperature control. The Worcester wave thermostat uses gas heat modulation to control heating, which works well and is more efficient. The boiler is on for longer at lower temperatures. So I wanted to do the same with the Nest, which says it supports Open Therm

Worcester Bosch uses an (apparently proprietary) EMS protocol to modulate the boiler. The thermostat was hardwired to the EMS socket in the boiler

I used those wires for the t1/t2 - 12v power supply from the Heat link to the Nest thermostat. I also powered up the Heatlink from the boiler 230v supply as per the Nest wiring diagram . The relay in the Heatlink seems to be redundant

So the 230V Live Out has a short link to the radiator LR and the Hotwater LR as per previous setup , as well as wired to the Heatlink

I connected the Heatlink to the EMS socket via this a Nefit Open Therm -EMS adaptor

https://myboiler.com/opentherm/worcester-bosch-openther

After powering up and the boiler operating, the issue is when the desired temperature is reached (say 20 degrees C) the thermostat controls the boiler by switching it on and off 2-3 times a minute. There does not seem to be gas flow modulation. The boiler blue light is always on and the boiler status seems be switching from "Waiting" to "Heating" - the flame light comes on ;. The radiator temperature fluctuates around 50-58 degrees. I can hear a clicking sound when the flame light comes on so there must be a relay switching the gas on and off

This doesnt seem to be satisfactory - I would rather revert to the default Nest configuration . But I would just want to check if the setup is OK

 

[jackthom]

Does it look like the Nest is changing the water temp target of the boiler as it should be, depending on how close the room temperature is to the setting on the Nest?

Must admit I don't like the idea of the pump running continuously and the boiler trying to run with a lower water temperature once the room thermostat is close to its own target temp.
Once the whole system has warmed up, if there is ever an overshoot beyond that low water temperature the boiler will shut down for a while and then attempt to re-start at medium power level, which if it happens too soon is likely to result in another overshoot before the power starts to ramp down.

There should be a boiler setting for anti-cycling time which will allow you to prevent the boiler trying to fire up before the system has had a decent amount of time to cool down a bit; ~10mins maybe?
The present 2-3 times a minute doesn't sound possible, let alone right.

 

[Mark72]

yeah I agree - it seems to be too precise, or over sensitive. It hits 20 degrees, then takes an hour and half to reach 20.5, and then shuts for a while. In terms of controlling temperature this is brilliant, but its switching on and off far too many times

Also ON/ OFF doesnt seem to proper modulation. My understanding is that the gas flame should be turned down, like you would do on a gas cooker to let something simmer

Maybe NEST doesnt do modulation very well, or the Open Therm / EMS adaptor is not working well. It would be nice if it overshoots to 21 degrees and then stop starts 3 - 4 times an hour . I'm sure a software update could sort that out

 

[jackthom]

The Nest should tell the boiler to lower or raise the water temperature depending on how much heat the house needs to get to the set room temperature. Can you see this setting changing on the boiler display?

It's completely up to the boiler itself to modulate the flow of gas to keep the water temp close to the target it has been given by the Nest.

The flame should be lower when the boiler has the water near the correct temp.

 

[picasso]

 

[Mark72]

The Nest should tell the boiler to lower or raise the water temperature depending on how much heat the house needs to get to the set room temperature. Can you see this setting changing on the boiler display?

It's completely up to the boiler itself to modulate the flow of gas to keep the water temp close to the target it has been given by the Nest.

The flame should be lower when the boiler has the water near the correct temp.

yeah sorry I see what you mean - I've been watching the water temperature on the boiler and it fluctuates between 47-58 quite rapidly . Maybe the problem is the the thermostat needs to settle down

Perhaps I should leave it a day or two

 

[Mark72]

Why have you got anything wired to the LR connections ?

thats how it was setup with the Worcester Wave Thermostat. If you disconnect the the radiator LR the boiler simply will not come on

 

[sjws1888]

yeah sorry I see what you mean - I've been watching the water temperature on the boiler and it fluctuates between 47-58 quite rapidly . Maybe the problem is the the thermostat needs to settle down

Perhaps I should leave it a day or two

Hi - Just wondering if this sorted itself out after leaving for a few days or if you had to do anything else to sort it? I'm asking because I've also got a worcester boiler and was thinking of getting a nest thermostat and have also come across that nefit EMS /opentherm adapter, so I was very interested to see whether you'd had any luck getting it modulating properly?

 

[Mark72]

Hi - Just wondering if this sorted itself out after leaving for a few days or if you had to do anything else to sort it? I'm asking because I've also got a worcester boiler and was thinking of getting a nest thermostat and have also come across that nefit EMS /opentherm adapter, so I was very interested to see whether you'd had any luck getting it modulating properly?

No it didn't work. I gave up after a while, and the boiler switching was driving me crazy . I also contacted Nest help on their forum, and they said nowt to do with them - please contact Nest Europe on Twitter !!!!

So I reverted back to the default setup - ON / OFF. It works pretty well because the boiler itself is modulating. I keep radiator temps at 65 C

So yeah I would still recommend NEST

 

[sjws1888]

thanks for the reply - interesting, I dont think I'll be going for the adapter then.
Cheers

 

[rbranco]

If it's going on and off check if you can rate the boiler correctly, ie if your radiator needs is 10kw and you have an 18kw boiler it will produce too much heat and overshoot, there may be a setting to derate it. This is regardless of modulation.

 

[Mark72]

If it's going on and off check if you can rate the boiler correctly, ie if your radiator needs is 10kw and you have an 18kw boiler it will produce too much heat and overshoot, there may be a setting to derate it. This is regardless of modulation.

thats an interesting point. I have felt that the ground floor radiators need to be double panel rather than single. They struggle when the temps drop below zero. But this (Open Therm Setup) goes back to last October when the temps were warmer .

So how do you derate it . Thats the job of the thermostat isnt it ??

 

[rbranco]

thats an interesting point. I have felt that the ground floor radiators need to be double panel rather than single. They struggle when the temps drop below zero. But this (Open Therm Setup) goes back to last October when the temps were warmer .

So how do you derate it . Thats the job of the thermostat isnt it ??

Nop, its a setting on the boiler, it's like a max power but smart wc thermostat is just controlling flow temps, problem is that it may go to max power when it first fires up and its too much. I know how to do it on vaillant but not bosch.

 

[SWA2]

I know it's now been 6+ months since this thread was active (and we're now in summer, so no one should be using CH!), but any updates on how the WB-Nest set-up is working, in particular whether the boiler is modulating even though the Nest isn't connected via OpenTherm?

My situation is I currently have a recent WB combi (8000 Style) with the EasyControl smart thermostat. It's worked well for the past year, but I'm adding underfloor heating for a new extension, which has to be set-up as a new zone, and the EasyControl is not compatible with multi-zone (except via Bosch's smart TRVs, but that's only for radiators, not UFH). I'm leaning towards using a Nest for the UFH zone and the EasyControl adapter so I can still use the EasyControl to control the radiators zone (and the smart TRVs), but it will regress to just on/off when calling for heat and I lose some of the functionality I have now when the EasyControl connects into the boiler using the EMS protocol via the EasyControl wireless key.

One of the main reasons I chose the EasyControl as the thermostat in the first place was I wanted to take advantage of various energy efficiency/optimisation capabilities, like weather compensation and modulation, so just trying to figure out what I will keep (and lose) in this new set-up. Anyone out there with a WB-Nest set-up have a view on this?

I'm also aware of the Nefit Opentherm Converter, but seems most people have had a bad experience with it, so not considering at this point.

 

[Chris L]

@SWA2 Did you manage to get any further with this and your underfloor heating?

my current setup is a 45KW Worcester 8000 which is working perfectly with my nest 3rd gen thermostat as an on/off controller only as I don’t think I have any way of choosing hot water temp so I’m just controlling that through the boiler controls itself.

after being let down by builders who have ripped us off and left us without a kitchen for months we’re finally near to being able to lay underfloor heating and I was going to go for water.

have you found any ways to set it up? I haven’t much experience of trying to set up zones with either Nest or the boiler (Worcester's instructions are none existent it seems in general)

also if you have an underfloor heating product then I’d love a recommendation as I haven’t a clue

Cheers mate