Setting flow temp on a Worcester Bosch 5000i - command ignored

[bittylicious]

I'm trying to configure home automation to essentially "call for heat" using EMS commands.

When trying to set the flow rate, e.g. using call boiler selflowtemp, it looks successful but the boiler just ignores the command. For instance, if it's set to 75° and I set it to 0 or 10, it will remain set at 75°.

I had a Bosch Easycontrol key installed and this is essentially the thermostat, i.e. a connected device tells the boiler what the selflowtemp should be (I can see it going between 0° and 75° when controlled by this). However, even with the key uninstalled, the boiler disregards the selflowtemp command.

Having done some debugging, I see these commands coming through when the key wants to call for heat (which sets the flow temp to 75°C), and when it doesn't need heat (which sets the flow temp to 0°C):

000+12:37:54.211 T 144: [emsesp] thermostat(0x18) -> boiler(0x08), W, ?(0x02E0), data: 01 4B 64 00 01
000+12:36:54.792 T 37: [emsesp] thermostat(0x18) -> boiler(0x08), W, ?(0x02E0), data: 01 00 00 00 01

These seem to correspond to (but please do correct me!):

call system send "0B 08 FF 00 01 E0 01 4B 64 00 01"
call system send "0B 08 FF 00 01 E0 01 00 00 00 01"

Has anyone ever seen this before? I'm only just starting my debugging, but it looks like my command can indeed set the flow temp where no other method I've found works.

The key also sends a few other commands which I haven't figured out yet, so would welcome advice:

000+12:39:36.503 T 272: [emsesp] thermostat(0x18) -> boiler(0x08), W, ?(0xE7), data: 00 02 00 64
000+12:39:36.565 T 274: [emsesp] thermostat(0x18) -> boiler(0x08), W, ?(0x02EA), data: 00

Finally, how would you recommend I actually control this using Home Assistant? Should I be creating some sort of sensor in the EMS-ESP web interface?

Many thanks for your help.

[proddy]

Perhaps the EasyControl is overriding the settings? Does changing the selflowtemp work with the thermostat disabled? Also note the boiler will only accept a flow temperature value that is lower than the current heating temperature (EMS/Bosch design).

[bittylicious]

Hi proddy. Unfortunately even with the EasyControl key physically out, I still cannot change selflowtemp. I don't think it's being set back - reading the values immediately after setting them results suggests they didn't change at all.

Noted about the flow temperature having to be lower than the current heating temperature. When I set a boiler temperature, the flow temperature changes to that same temperature on the next EMS update. The problem is that I cannot set the boiler temperature to be below 30°C (I'm aiming for "full off", i.e. zero).

I did read a post-manufacture document a while ago suggesting that if you used an external thermostat (e.g. the EasyControl key), the boiler needs a factory reset when changing this. I don't really want to do this as I'm not confident to recommission the boiler.

[proddy]

does the boiler temp change (and max pump %) when you enable the forceheatingoff function in EMS-ESP?

[bittylicious]

No, neither changes. The functionality does work though - I it stops the boiler from firing - but it doesn't change any flow temps / max pump percentages. It is a solution, but hacky and I prefer if I can actually force a change of the flow temp which my command seems to do.

[MichaelDvP]

@proddy We always set selflowtemp with 0x1A telegram. Seems some of the newer ems+ boilers uses 0x2E0 for commands. But without product-id we can not change. Also unclear is offset 2, could be pump power or max burner power.

[bittylicious]

This does seem to work quite well to simply set the flow temperature. It'll set it, on my system, up to 75°C, which is what I have the max temperature set to.

Because it's a non-raw value, it can also be nicely set in HomeAssistant.