Our new house has a pretty recent Bosch Greenstar ii boiler that runs on oil. The £6grand the previous owner forked out to have it installed (I found a receipt) included a rudimentary control system that basically means it’s “on” or “off”. There’s no zoning and no room thermostats.

Due to carpet bombing style application of insulation, some of the rooms are really warm and others can chill wine.

I’ve decided to fit a pile of smart TRVs and a smart thermostat/gateway.

Bosch, being Bosch, use a proprietary comms protocol in the boiler called EMS and it has no OpenTherm interface. But: they sell a conversion interface in Europe that I’ve fitted and it would appear the gateway is talking to it. So this afternoon I removed the shunt across the boiler stat terminals hoping the gateway and all the TRVs would take over.  And… diddly squat happened, apart from the place started to get colder despite demand from every room. Anyone got any ideas how to troubleshoot this or tried to drive a Bosch boiler with a moderating controller?

I foresee some sort of expert being required, but I don’t anticipate a plumber being equipped to deal with this sort of thing.

I’s say you need an appropriate nerd for the brand of TRVs/stats – what are they?

Netatmo. French tech sending instructions to a German designed British boiler. What can go wrong?

Have you tried just wiring the gateway directly to the boiler I.e. on/off control but no EMS?

The netatmo boiler cables are just connected to a relay that sets them to be continuous or not for boiler on/off (I can’t remember which way round, but I think it might be reversible in settings).
I don’t have Bosch, but on our boiler the netatmo connections just go in place of the shunt rather than via a second controller.

It’s the modulating Netatmo thermostat. Which afaik talks OpenTherm not on/off like the non-modulating version.

Have you found/tried these? Heating / home automation nerds generally seem to love helping each other out;

https://forum.netatmo.com/

https://www.facebook.com/groups/netatmo.support/

I might have this completely wrong, but oil boilers can’t modulate. They’re either on, or off.

edit ignore me. That’s not your question

@northernremedy. You might be onto something though.  I wonder if the Netatmo device is sending a heat demand in kW or °C and the boiler is going “I’m not quite sure what you mean, is that on or off?”

What converter did you use? Was it by any chance the Nefit EMS-OT one?

Worcester Bosch and OpenTherm

Bad news if it is, they seem to be very flaky and most folk have been unsuccessful in getting their boilers to modulate. How do I know? I’ve been banging my head trying to come up with a solution which isn’t Easycontrol. TL:DR there isn’t really one unless you go down the full on Greenstar Sense II with weather sensor route. No other system is compatible barring one which was mentioned on here but was internet based so ruled out pretty quickly for my needs.

It was Tado I was thinking of, I think.

I don’t get why opentherm is coming into it – does it do something other than modulate the output of the boiler down? Since oil boilers can’t modulate are either on or off, what’s the point?

Jusr wire the on / off stuff into the heating controller and let that do weather compensation and the rest of it. You may want to check the controller has an oil setting to avoid short cycling.

I don’t get why opentherm is coming into it – does it do something other than modulate the output of the boiler down? Since oil boilers can’t modulate are either on or off, what’s the point?

tbh I assumed OP had done his homework as was talking about EMS/opentherm, bought the interface kit & a modulating thermostat. But, possibly not!!

Jusr wire the on / off stuff into the heating controller

yeah, depends whether the Netatmo modulating thermostat actually has this option though or can only be used with an OpenTherm boiler? My Drayton thermostat had a removable OpenTherm module so could work with either… no idea about Netatmo tbh… not a brand I see mentioned much or at all really (when you look at the price of the TRVs you can see why maybe!)

Yeah it’s that nefit converter, which is actually a bosch part (though not in any of their catalogues). I was more interested in getting the data out of the boiler (there’s a LOT of data it captures) than actually being able to switch it on or off. I’ll swap the modulating stat for a conventional one and start again.

The netatmo kit list price is horrendous, but you can find it loads cheaper if you hunt. Their approach to data and the homekit integration is what sold it to me. It’s like a properly integrated version of evohome.

Not heard of netatmo. I’ve installed wiser which seems to be pretty great so far. I know you can integrate with homekit and pull a load of data – it’s on my long list of things to do.

Edit: I didn’t mean homekit. I mean the opensource automation thing, that i’ve forgotten the name of!

I was more interested in getting the data out of the boiler (there’s a LOT of data it captures)

ideally wondering whether you can use a regular on/off smart thermostat to control the boiler and use the EMS connection (is there a separate one on the boiler?) for output only. Does the Nefit thing connect to WiFi & log data in the Bosch cloud? Otherwise looks like there’s a Python library to access the API https://pypi.org/project/nefit-client/ (also a Home Assistant integration which does the same but is obviously much simpler to use!)

Their approach to data and the homekit integration is what sold it to me. It’s like a properly integrated version of evohome.

Homekit integration is good as it (should) mean it can work locally, rather than being dependant on cloud/internet access like a lot of other systems (including this one if you’re not an Apple user!!)

Edit: I didn’t mean homekit. I mean the opensource automation thing, that i’ve forgotten the name of!

Home Assistant? This is what I use for DW – works great! (It actually can integrate with HomeKit without HA, but you need to run a HomeBridge server, so you might as well go the whole-hog IMO!)

Home Assistant – yep that’s the one.

The nefit device simply a protocol switcher: from Opentherm to EMS. I could then plug in a rasprian device into that and get the data out if i use the netatmo to control on/off (which it looks like I’ll have to do).

I didn’t want to end up dependant on some remote cloud service over our starlink connection to run my heating. Homekit’s local availability means I can build automation in there as a failover. Even then I’m contemplating a damned great “boiler override” switch on the wall of the utility to spool it up if it all goes wrong.

Ah I see, I was getting confused as someone else had mentioned modulation and assumed they did in fact do that.

Really you should be wiring the controller in as per normal then pulling the data through EMS using your converter, trying to use them in tandem is going to result in tears I think. If they are in fact Bosch made then they didn’t do a very good job as nothing seems to control properly through them.

I fixed this. Replaced the stat with the non-modulating version and all is now well. Thanks for the pointers.