If you are using Madoka for thermostat control, rather than leaving water temp only, then I suggest you go into the Madoka settings and reduce the brightness of the screen and the blue ring light that indicates the heating is running.
I reckon the LEDs affect the reported temperature by at least 1C compared to local ambient. I’ve configured a -1C offset in the MMI for this.
In the case of the blue ring light, I was seeing a very quick drop of -0.5C as soon as soon the heating switched off. 
It played havoc with the thermostat control when I disabled modulation.
I’ve seen more consistent readings since changing these settings. I’ve turned it down until the values are just visible in daylight. There is also a “hotel mode” that switches off the backlight and blue light. I haven’t enabled that as I do like to be able to see the current temperature