Hi All,
I’m running a Sonoff TRVZB and have a schedule set up. As you can see the TRV is set to 18 but is saying the room is only 17.7 but has not changed to heating. Is there some sort of tolerance it waits for before changing and opening the valve? If go to manual mode and then change to 18.5 and back down to 18 then it keeps the valve open.
There is nothing unusual about this situation. This is because 17.7 is subject to rounding up and here it just happens to be 18. In the device settings you have the option “Temp calibration”. There you can lower the temperature slightly and you will be fine.
Ah ok that makes sense, I didn’t realise it rounded to the nearest whole number to enable / disable heating.
For some time this was not the case. Users were unhappy that the measurement was rounded. Well, now they have without rounding 
I think it depends on the device. The measurement from the same external temperature sensor on my NSPanel screen displays rounded, while NSPanel Pro displays the measurement with a decimal point.
There is some sort of overshoot/undershoot allowed before it changes, so as to not be too annoyingly noisy and use battery up. I’m not sure how big the value is but both my other types of smart valve have it and I can’t set this amount in Zigbee2MQTT either. If I wish to open or close the valve I just either put it really high or really low respectively. I suspect it’s a hardware thing on the valve itself.
It must be something like a 1c overshoot if that’s the case. I could understand 0.5c but 1c is quite big in my opinion.
I’ve got a Sonoff USB arriving this week and will eventually be using Zigbee2Mqtt in HA so will be doing similar to you.
I plan to use a temp sensor in the room to trigger the stat and set it to like 25c and 5c based on the room temp.
For now until that stick arrives I’m stuck with the eWeLink app.
If you’ve already got a temperature sensor just have in turn on to MANUAL 30°C with an automation when it is too cold or OFF when too hot exactly as you determine.
You can actually do that now if you have a device that can run eWeLinkCube (IHost and NS Panel Pro I think) as the temperature of the radiator is obtainable using Node Red, although I’m not sure it updates frequently enough to make scenes with.
I did try it via scenes in the eWeLink app but it didn’t appear to trigger it reliably so went back to auto schedule.
Zigbee2MQTT with home assistant should solve majority of my issues hopefully.
Possibly, although you may find they don’t update the Zigbee network , whoever runs it, with the current temperature often enough and end up using a separate sensor yourself. I think the temperature sensor probably wakes up fairly often and checks the temperature but only updates the Zigbee Network every now and again in order to save energy.
Remember about hysteresis and about the fact that heating systems with water as a medium have quite a bit of inertia, so overly ‘nervous’ responses from thermostats do nothing. Unfortunately, the hysteresis scope in the Sonoff TRVZB is not adjustable.
Hi, the hysteresis is fixed at 1°C, so if you have it set to 18°C it will only start heating when it drops below 17°C. I have been told by eWeLink support to contact the ITEAD manufacturer, so we will see if with some other firmware they will then allow the eWeLink APP to override the hysteresis to less than 1°C, it’s too big a temperature difference for thermal comfort.
