Using Bai/HeatingSwitch to control heating?

[neoc41]

I've got a Vaillant EcoTec Classic connected to ebusd and through MQTT auto-discovery to HA. Lots of values coming through but the main reason for getting ebusd was to control the heating of the house. I'd like to get rid of the simple on/off thermostat the house came with.

Apparently I did not do my research well enough before buying the adapter because of course I've since found multiple posts saying that ebusd isn't meant to directly control the boiler. Now before I replace it with a different solution I was wondering why using Bai/HeatingSwitch and switching it on and off depending on the temperature in the house is a bad idea?

[JonesGW-MGD]

That parameter is the same as D.023 on your boiler panel - and it sets winter or summer mode. I don't think that is going to give you what you want.

It's not impossible to control a heating system using ebusd but you need to bear certain things in mind and you won't find something 'out-of-the-box' so it requires digging a bit deeper and understanding what is going on - which frankly if you're going to use automation to control a gas boiler - is probably not a bad thing!

First, not all messages are writable - some are read-only. Not all writable messages are set to be writable by default. Not all messages you think should be writable are - because Vaillant might use another message to write something - like setMode for example and another to read it such as hwctempdesired or flowtempdesired

Maybe start by searching the forums for use of setmode or setmodeoverride (even though setmode has been made writable in installer mode in hcmode.inc since this commit: john30/ebusd-configuration@ba4c749

Finally, bear in mind that most ebusd users do not use ebusd to control their heating appliances, and the vast majority simply benefit from the data they can pull rather than trying to change anything. Moreover, those that do write certain commands (I use it to change the heat curve out of convenience) don't endeavour to replace the other controls on the bus, rather use ebusd to complement them. So that may limit the people that can help you.

[neoc41]

Thank you for your reply and thorough explanation

I've read up a bit on using SetMode but it is still unclear to me which parameter is best adjusted to enable/disable the flow of hot water through my radiators to change the temperature in the house?

[JonesGW-MGD]

For heating, I'd focus on the second parameter - flowtempdesired

Assuming you're going to have external HA-enabled temperature monitor(s) you probably want to emulate a super-simplistic version of the Vaillant heat curve:

The 'trick' with central heating is to run the flow temp as low as possible that still makes the room/house as warm as you want it as quickly as you want it - it's going to depend on where you live, the seasons, and on the size of your radiators and your general comfort levels.

But as an example, if you find that a flow temp of 50 deg gets, and maintains, your room/home to the the temp you want - say 20 degrees, then set the desired to this, and when it is reached, lower it. You want to ensure you are not switching the boiler on and off frequently because you heat too quickly, it cools and you heat again ('cycling')

But you also need to monitor other side effects - so you don't want the flame on when the pump is off too much (although you do want some of the opposite of this - called 'pump overrun' so that the heat doesn't build up in the boiler but is dissipated) - and your boiler may have anti-cycle and pump re-start timings too. Also boilers are designed to operate at lower than their rated output 'range-rating') and also modulated either within their rating or their range ratings. And then you need to worry about what you do with hot-water. (Does your boiler heat a cylinder or is it a combination boiler for example?) - which is why it is relatively complicated to just control it using ebusd and overriding the standard controls.

[neoc41]

Thanks for the explanation. It makes a lot more sense now why so many people seem interested in controlle flowtempdesired!

But just to confirm I've understood correctly - with ebusd it is not possible to emulate the simple on/off switch that my thermostat sends depending on whether the thermostat temperature is above or below its set level?

[JonesGW-MGD]

Maybe I'm missing something but if that's all you want to do - you don't need ebusd?

You've not mentioned what thermostat you have but pretty much any boiler can be 230V- or bus-controlled. (For example if you had a Nest, or Hive or some other brand of 'smart controller' then they would use 230V switching and not ebus.)

You can emulate these 'smart controllers' and control via HA. (they are not very smart at all as they are just on/off - which sounds like it is what you want) Wire a Normally Open relay that you can control using wifi or zigbee or whatever from HA like Sonoff or Shelly to L-E-N on its supply side and between RT ('Room Thermostat') and L on its output side. (If your boiler had no external thermostat you will probably have to remove a link wire labeled between 'RT' and '24v' elsewhere on the boiler PCB.)

Caveat - don't play with mains voltage if you are not comfortable doing so - you might fry either yourself or the boiler!

Use HA automation to switch the relay based on some temperature sensor. You will probably want to build in some hysteresis loop - which is nothing more than lengthening the gap between set-point on and off. So for example if your desired temp is 20, you want to make sure the relay doesn't fire on and off if the temp moves from 20.1 to 19.9 and back to 20.1 for example - otherwise you'll quickly wear out your boiler.

Manufacturers like Vaillant developed bus control recognising that most people want much more sophisticated control than 'on-off' but if you don't need it, don't use it!

Alternatively, you can emulate an ebus-enabled controller, as posted above - and one method that people on these forums have done that is by sending setmode or setmodeoverride commands - but bear in mind you need to do this every few minutes, even if the desired temp doesn't change or the boiler will override it. If you are still interested in going down this route - this might be a good starting point: john30/ebusd-configuration#170

Or you can probably set up a programme of on and off times, holiday periods, vetos etc. by emulating different commands. (But you may need to upgrade your thermostat/controller to be able to support these messages which might be counter to what you actually want to do.) Check out the zone 1 - z1xxxxxx messages in some of the 15.xxx files for example, such as w,,,Z1DayTemp,desired temperature zone 1,,,b524,020103000700,value,,EXP,,°C,day setpoint for zone 1 or w,,,Z1QuickVetoTemp,quick veto temperature zone 1,,,b524,020103000800,value,,EXP,,°C,manual override setpoint for zone 1 .
Check out posts like this: #764 (comment) or #530