Replace smart thermostat with WiFi relay?

[MikeF]

I have a Worcester Bosch combi boiler, controlled by a Drayton Wiser smart thermostat / hub, for which I've written Domoticz scripts, so that I can set schedules and the setpoint temperature, and read the current thermostat temperature.

When heating, I've noticed that the heating relay in the Wiser hub regularly turns off every five minutes or so, and turns on again after about five minutes.

I have two concerns about this:
1. that the heating is taking longer to reach the setpoint temperature
2. the frequent on / off switching of the boiler.

I am contemplating replacing the Wiser hub with a WiFi relay (e.g., Sonoff) and temperature sensor, controlled by my Domoticz scripts.

Can anyone see any issues with this? the boiler will be constantly on until it reaches the setpoint temperature - after all, this presumably what 'dumb' programmers / timers do.

Mike

[waltervl]

You better check with Wiser why it would switch on/off so regularly.
Is you boiler able to modulate instead of simple on/off? Perhaps there is a setting wrong.

[marcojpolet]

Hi Mike,

The behaviour you describe seems to be to avoid a big overshoot? I'm using the Domoticz SVT plugin (smart virtual thermostat). This works very well and learns the characteristics of the room. So it will try to put in as much energy as it thinks is needed based on current temperature, outside temperature, and previous heating cycles. I have several rooms defined all using their own SVT hardware.

Regards,
Marco

[MikeF]

You better check with Wiser why it would switch on/off so regularly.
Is you boiler able to modulate instead of simple on/off? Perhaps there is a setting wrong.

Thanks - I'll need to investigate.

[MikeF]

Hi Mike,

The behaviour you describe seems to be to avoid a big overshoot? I'm using the Domoticz SVT plugin (smart virtual thermostat). This works very well and learns the characteristics of the room. So it will try to put in as much energy as it thinks is needed based on current temperature, outside temperature, and previous heating cycles. I have several rooms defined all using their own SVT hardware.

Regards,
Marco

I'll have a look at that. My system is currently very simple - one room thermostat (I've bought two radiator thermostats, but I haven't installed them yet).

[MikeF]

Having read my boiler's instruction manual, I am satisfied that it is a modulating boiler.

However, it appears that the Drayton Wiser thermostat / hub is doing its own modulating, but as there is no feedback from the boiler (the hub just switches mains live to the boiler), it would suggest that it is pre-empting the boiler's modulation (and possibly switching on / off too frequently). Hence my thoughts about replacing it.

[waltervl]

If you buy a new thermostat buy one that is compatible with your boiler.

[MikeF]

If you buy a new thermostat buy one that is compatible with your boiler.

I want to be able to be able to control / set a thermostat / boiler relay locally, via Domoticz (pref. wifi / MQTT) without having to go through external servers (which Bosch EasyControl does).

[waltervl]

Check if your boiler supports the Opentherm protocol (perhaps with a converter) then you have more options.