Good programmable thermostat? (not Drayton Digistat!)

[CharlesElliott]

Having had two of the 'original' Drayton Digistats which worked very well, I've now had it with the latest model that tries to guess whether the heat should be on or not and gets it wrong most of the time.

What's a recommended digital thermostat, 7 day programmable, that doesn't have built in intelligence, or if it does you can turn it off so that the call for heat works at the temperature you actually set it?

Thanks!

 

[D_Hailsham]

I've now had it with the latest model that tries to guess whether the heat should be on or not and gets it wrong most of the time.

Can you elaborate, please?

 

[CharlesElliott]

I think it is fairly well documented that the Digistat+3 uses logic to estimate overshoot. So, for example, if you have the temp set to 20 deg, it will turn the heating off at 19.3 deg because it expects the temp to continue to rise. The problem is that it's logic doesn't work in the real world. It is supposed to calculate this based on 'learning' in the first couple of weeks, but everyone's experience that I've heard says it doesn't really work.

It drives me mad!

 

[tonyheat]

Having had two of the 'original' Drayton Digistats which worked very well, I've now had it with the latest model that tries to guess whether the heat should be on or not and gets it wrong most of the time.

What's a recommended digital thermostat, 7 day programmable, that doesn't have built in intelligence, or if it does you can turn it off so that the call for heat works at the temperature you actually set it?

Thanks!

Assume you are referring to stats with optimisation (i.e adjust start time depending on tempreture), and Time Proportional Integral control -When the room temperature approaches the set point, it then calculates how many minutes are required within each firing period to satisfy the set temperature.

I used to use the Honeywell CM67, or more various Siemens, and do not have a problem with Proportional control. However on both ranges you can turn off TPI within the menus.

 

[CharlesElliott]

Thanks. I agree the idea is a good one, but it needs to work. The Digistat neither works (in my experience), nor can be switched off.

 

[D_Hailsham]

The Honeywell CM9XX prog stats do what it says on the tin.

I've had a CM927 for over five years and it holds the temperature rock steady at whatever it is set to. Optimization (automatically varying the ON time) also works very well.

Are you comparing what the Drayton thinks the actual temperature is with a separate thermometer?

 

[CharlesElliott]

A typical situation at the moment is setpoint at 20.0 deg, temp shown is 19.3 deg and there is no call for heat. This is because it thinks that the actual temp will keep rising following earlier call. So you end up putting the temp up to 20.5 deg to get it going.

 

[Sirbendy]

That's odd. I have a digistat+3, and it doesn't have that issue. Set temps are reached and held fine.

 

[doitall]

Honeywell cm907 if you want wired, or cm927 for RF.