Drayton Digistat +2 acting weird

[Bratters]

I have a Drayton Digistat +2 controlling some electric heating in my house. It's acting a bit weird and I wonder if anyone knows why...

Basically, I assumed it's a straightforward thermostat setup: it's supposed to call for heat when the actual temperature is lower than the set 'target' temperature, then stop calling for heat when the set point is reached.

What it actually does is sometimes stop calling for heat even when the room is still below the set point (at least 1C below sometimes, even though the display and sensor works to 0.1C resolution). Then at other times, it will do the opposite and keep calling for heat even when the actual temperature is nearly 1C over the set point.

It's not that it's wired up wrongly - even the little flame icon which indicates 'call for heat' shows that it's sometimes calling for heat when you wouldn't expect it to and vice versa.

The overall temperature isn't usually more than a couple of degrees out, but I'm just curious as to why it works like it does really.

 

[Diyisfun]

Have you got it linked to the timer & the times are clashing?

 

[Bratters]

No - even when I've tried using it completely 'stand alone' it seems to indicate call-for-heat at times when the temerature is above the set-point, and sometimes not call-for-heat even when below the set point.

It's not a major problem as the temperature is never too far out as I said, but just not as accurately-controlled as I thought.

 

[BS3036]

I have no idea of the real answer - but any switch of this kind is likely to have a built-in hysteresis to prevent turning the boiler on and off too often. A really intelligent system would also compensate for the delay from switching till an effect is felt, though I doubt that is happening here.