Reading Sontex 789 with EmonHP

Hi again,
I tried connecting my Sontex 789 to the emonHP today (still waiting for installation of electrical meters). The emonHP is successfully communicating with, but the info from the Sontex 789 mbus don’t seem to be coming through correctly, see below from the emonHP log. Any ideas @TrystanLea? Thanks very much!

2022-11-15 20:17:30,748 DEBUG    MBUS       Invalid MBUS data received 146 bytes 718.4 ms
2022-11-15 20:17:30,750 DEBUG    MBUS       Decoded MBUS data: {"Energy": [776, "kWh"], "Energy2": [349, "kWh"], "Energy3": [117, "kWh"], "Energy4": [0, "kWh"], "Energy5": [0, "kWh"], "Energy6": [0, "kWh"], "Energy7": [0, "kWh"], "Energy8": [0, "kWh"], "Energy9": [0, "kWh"], "Energy10": [0, "kWh"], "Energy11": [0, "kWh"], "Energy12": [0, "kWh"], "Energy13": [0, "kWh"], "Energy14": [0, "kWh"], "Energy15": [0, "kWh"], "Energy16": [0, "kWh"], "Energy17": [0, "kWh"], "Energy18": [0, "kWh"]}
2022-11-15 20:17:30,750 DEBUG    MBUS       7171 NEW FRAME : 
2022-11-15 20:17:30,751 DEBUG    MBUS       7171 Timestamp : 1668543450.029469
2022-11-15 20:17:30,751 DEBUG    MBUS       7171 From Node : heatmeter
2022-11-15 20:17:30,751 DEBUG    MBUS       7171    Values : [776, 349, 117, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
2022-11-15 20:17:30,752 DEBUG    MBUS       7171 Sent to channel(start)' : ToEmonCMS
2022-11-15 20:17:30,752 DEBUG    MBUS       7171 Sent to channel(end)' : ToEmonCMS
2022-11-15 20:17:30,988 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy 776
2022-11-15 20:17:30,989 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy2 349
2022-11-15 20:17:30,990 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy3 117
2022-11-15 20:17:30,990 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy4 0
2022-11-15 20:17:30,991 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy5 0
2022-11-15 20:17:30,992 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy6 0
2022-11-15 20:17:30,993 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy7 0
2022-11-15 20:17:30,994 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy8 0
2022-11-15 20:17:30,994 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy9 0
2022-11-15 20:17:30,995 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy10 0
2022-11-15 20:17:30,996 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy11 0
2022-11-15 20:17:30,997 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy12 0
2022-11-15 20:17:30,998 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy13 0
2022-11-15 20:17:30,999 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy14 0
2022-11-15 20:17:30,999 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy15 0
2022-11-15 20:17:31,000 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy16 0
2022-11-15 20:17:31,001 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy17 0
2022-11-15 20:17:31,002 DEBUG    MQTT       Publishing: emon/heatmeter/heatmeter_Energy18 0
2022-11-15 20:17:31,003 INFO     MQTT       Publishing 'node' formatted msg
2022-11-15 20:17:31,003 DEBUG    MQTT       Publishing: emonhub/rx/heatmeter/values 776,349,117,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

Edit - formatted text. Moderator

It looks like it is decoding something, what are you expecting as the values?

Please post your emonhub config (use the preformatted button to format it correctly)

Hi Fiona

Have you put all the following in your emonhub config.?

Noting the Sontex 789 needs some extra config tweaks as per towards the bottom of the heat meter section.

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Yuck! editing the interfacer itself is not great advice! @TrystanLea @glyn.hudson. Is this still correct with the recent updates?

Thanks @borpin and @Zarch! How do I get to the EmonHubMBUSInterfacer file, is it on the SD card? I don’t see where to navigate to it when logged into emonhp.local.

Going to be honest here and say that I don’t actually know what the EmonHP is. Is it just an RPi?

@Gwil @TrystanLea @glyn.hudson - if so, how is SSH achieved?

EmonHP is the heat pump monitoring system, although maybe that’s not your question @borpin. I assume it’s a raspberry pi, but I know approximately nothing about any of this!

Yes I found that but I don’t know what the EmonHP box is. I guess a Pi, but don’t know. You may need to connect a keyboard/monitor to it to get SSH access to it.

As far as I know, it was originally emonTx-based, but now it’s a RPi and a Shield with some emonTx-like facilities.

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Yep: GitHub - openenergymonitor/HeatpumpMonitor: Open-source Heatpump Monitor

Scroll down to the words and pictures.

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Hi @frh

I’m able to remotely connect to your emonHP and configure the Sontex for you. Could you let me know when the Sontex is connected? It maybe easier to do this over email? Please drop us an email when the Sontex is connected and you’re ready for us to configure it: [email protected]

This is correct. Getting the Sontex 789 into the right mode is a bit awkward. This only needs to be done once.

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Yes, but it would be better then with it’s own interfacer, as changing this prevents emonhub being updated from Git!!

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The change is only temporary, 0x5b just need changing to 0x7b then back to 0x5b. This advances the data page of the meter. Once up and running the interfacer will be back to normal and will update fine from github.


Could you do a small setup script, that could be run on install?

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Yes, that would be good.


Thanks all for your help. @glyn.hudson did the update remotely, and now my plots look like this:


Great, you flowT looks nice and low and your dT looks good. It’s interesting that the flowT drops overnight, do you have an overnight setback set? What heat pump is this?

We have it set at 20 deg in the day and 17 overnight. So far the house only drops to about 19 overnight though. It’s a 5 kW Arotherm+. I thought DT was bit low? I’ve been following @Zarch’s adventures in changing pump speed, might have a fiddle around with that at some point.

Fiona Hughes


Green Heat Coop

[email protected]

Twitter @greenheatcoop

I’d stay as you are for the moment Fiona.

Heat Output = Specific heat capacity x flow rate (l/s) x (flow temperature - return temperature)

If you follow Adams graphs too it certainly seems to be an Arotherm thing that it uses the higher flow rate whilst squeezing the DT to achieve its output.

If your unit and house is anything like Adam and I, the minimum 2.5kW ish that the unit can kick out is currently too much load for the house when 10C outside.

With 0C forecast for the coming week, let’s see how that all goes.

From what i’ve played with, i’ve had ‘slight’ success in high COP dropping the pump speed . But I think i’ve gone too far slowing it down and some of the rads are struggling.

Max flow rate in the book is 860 l/h (14.3 l/m) - although not convinced as Adam has seen 900 l/h
Min is around 430 l/h (7.2 l/m)

I will continue to play.
But I don’t think messing with DT when it’s 12C outside is the best timing.

Bottom line, room comfort is king, 0.2 of a COP doesn’t matter. :upside_down_face:

Out of interest, who installed yours Fiona?
Have they done anything special with regard the rads? Do you have a buffer?
Have the rads been balanced? Or are they fully open?
I’m currently trying to get my head around the best approach for the rads.
I can’t seem to find any definitive guidance for low temp, DT5, heat pump rads.

Everything seems geared towards boilers and DT20.

PS. Shall we start a separate “Vaillant Arotherm Owners” thread, rather than fill other threads with Arotherm anecdotes?

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As Mick said I wouldn’t worry too much about dT, my dT is about 1.6. I can’t adjust the pump speed manually, it’s set by the heat pump (5kW Samsung). It still seems to getting decent performance with this low dT. A low dT will make the heat more uniform which makes radiators more comfortable and negates the need for balancing which results in constricting flow.