Drayton Digistat +3

18 Jul 2007
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United Kingdom
I've recently replaced my Honeywell DT200 with a Drayton Digistat +3 as I wanted a programmable unit (don't like coming home from work to a cold house :D)

This seems to work fine, i.e. it switches the heating on and off when it gets cold and hot, however I wanted to confirm whether the behaviour of it is normal.

With the Honeywell set to, lets say 21, the heating would run until it got to 21.5 then would switch off, and then would come on again when the temperature dropped to 20.5, as you would expect from a basic thermostat. Naturally there is a bit of additional temperature increase after the system has switched off as the radiators are still hot.

With the Drayton, lets say you set it to 21 when the house is currently 16, it will run constantly until the temperature reaches around 19 and then will switch off. After this the system will cycle on and off, at a guess roughly 30% on and 70% off, gradually increasing the temperature until it reaches 21, minimising any additional increases once it's upto temperature. Once upto 21 the heating will come on for approximately 2 minutes at a time, probably once every 20 minutes, and the temperature will remain pretty constant and a lot closer to the set temperature than with the Honeywell.

While this gives a much more accurate and stable room temperature I've never seen this kind of behaviour from a thermostat before, is this normal for this particular model? Will this cause more wear and tear on the boiler with it cycling on and off a lot more and often for just a couple of minutes, or am I concerning myself over nothing?

Oh, and sorry for the excessively long post :D
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I dont recognise that as a design feature of your stat.

What hysterisis setting have you put into the unit?

You should set it for 1° C or even 0.5° if the unit allows it which I cannot remember. I have a feeling they come set at 3°.

I like those units although they are not that easy to set up unless you have considerable experience of them.

The instructions are not very clear and its easy to encounter unexpected problems.

You have to start by deciding how many switching times a day are required for example.

The manual supplied suggests the hysterisis is set to 0.5° and there seems to be no way to adjust this either through the user menu or the installer menu. I'd rather leave this at 0.5° than have it any higher anyway.

I currently have it set to 6 switching times a day due to an odd shift pattern I work, but I notice the same behaviour even if I disable the programming and operate the thermostat in manual mode, i.e. set the temperature to 21° as you would do with a simple non-programmable stat.

I might pick up another one this afternoon and see if it exhibits the same behaviour.
The hysterisis is set in one of the setting codes like 04 or 05 etc.

You should check thats correct as a first step and 0.5 is usually best.

Its also got an "offset" setting which should be at "0" but was at "3" on one I was setting up last week.

Those setting codes are very important to start off correct to avoid problems.

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Definitely no changeable hysterisis on this. The model I have is the zero volt version, maybe the hysterisis is only changeable on the mains voltage model? All other settings such as the offset are correct.

The main thing that concerns me about this over the Honeywell stat I had previously is the frequency at which it turns on and off.

When my house is upto temperature in the evenings, for example, this will turn on and off every 14-15 minutes, staying on for just 2-3 minutes at a time, whereas my previous stat would turn on roughly once an hour for about 12 minutes.

Is it bad for the boiler to run in short bursts so frequently or am I worrying unnecessarily?
I think you are being rather paranoid!

Clearly 2-3 min every 15 min will give closer control of the room than 12-13 min every hour by which time the room will have cooled considerably.

I cannot imagine a "zero volts" version! The ones I have set have been either wired or wireless and both powered by two AA batteries!

Both types had an hysterisis setting in the setup menu. They probably dont call it hysterisis and have their own stupid name like on-off gap setting.

An interesting point is that you ONLY load the new value into the register when you right click.

Its easy to left click and then you end up with the selected value not being saved.

The instructions are significantly lacking in correctness. It would be so easy for me to write them clearly.

An example is that it tells you how to program the change times and new temperatures but FAILS to tell you that first you MUST set the number of changes per day!

I still like them even if I am one of very few who can set them!


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