Honeywell DT90E

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Hi, does anybody have any experience using Honeywell DT90E thermostat? I just got one, connected to Ariston combi boiler which has auto function for self-regulating of the water temperature in the radiators. Would it be a good idea to have it activated with this thermostat?

I only been using the thermostat for a couple of days, not running much with the weather getting nicer. Maybe three or so separate days. I read it has to learn, so it might still be adjusting, but my issues is that it overshoot the set temperature by 0.5 degree. Which is expected according to something I read somewhere , so that would not be a problem on its own, only it will not stop calling for heat after it reached the set temperature (and is in the overshoot).
So let's say it's set for 21 degrees, it will go to 21.5 and keep calling for heat for minute every ten minutes to keep the temperature at 21.5. My understanding was it will heat to 21.5 (with the 0.5 degree overshoot). Then because it is over the set temperature, 21 degrees, will stop and not trigger the boiler until the temperature drops below 21.
I know 0.5 degree doesn't look much but over time it mounts up and honestly seems wasteful to me which is defeating the whole object.
So does anybody know, is it suppose to stop calling for heat after it reaches the set temperature or keep heating to the extra 0.5 degree? In that case it's pointless and might as well set it to half a degree temperature lower than I want .
Thank you for any input you can give and sorry for a long post
 
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Thank you for your replies. But does anybody know if it is suppose to stop calling for heat after it reaches the set temperature? And if it overshoots then just stop and wait for the temperature to drop?
I will give it more time to settle, just wanted know whether I have a potential problem on my hands.
Thanks.
 

CBW

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Yes, once the temperature has been reached, it should no longer call for heat, is this not happening? It’s probably accurate to +/- 0.5 degrees.
 
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Every time I set a temperature it overshoot 0.5 degree and keeps calling for heat to keep it at 21.5 instead of 21 degree for example. So when I get too warm I turn it down and then when the temperature drops to half degree above my new target temperature it starts calling for heat again. Is that what it is suppose to do?
Thank you.
 
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CBW

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No it shouldn’t call for heat unless it needs to. I know it’s only 2 wires, but has it been wired correctly? Failing that i would be thinking it’s a faulty unit.
 
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Mine used to overshoot by .5 of a degree. Once target reached, it would come on every 12 minutes I think, to maintain the temperature. Are you sure it's actually calling for heat and it's not just the overrun?
 
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I think it is calling for heat, the flame symbol comes on and boiler kicks in. Hoping its just the learning period. It probably won't get much of a chance to learn untill winter now . I guess time will tell.
 
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I take it your's is wired, ie, 230V, do you know if that's a permanent live or a switched live (say from the timer) and if a switched live are there also batteries in it to keep it "alive"?.
 
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I had the slightly different DT90, no green button but otherwise the same. Mine took nearly 3 weeks to finish learning and stop overrunning but yours may take longer if its not coming on very much given the weather at the moment. I found the thermostat worked well keeping the house at a stable temperature but I couldn't live with the very loud click everytime the thermostat turned on/off. The minimum was 2 clicks every 10 minutes all night long! In the end I sent it back.
 
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Thank you all for your replies. So it seems it might just need more time (I'm not the most patient person but will have to get over myself this time). You're right about the clicking, a lot of people complain about it. Read somewhere it might depend on the wall type, different materials make it sound louder. Mine is in the living room and with tv on I can hardly notice it. So fingers crossed and thank you all.
 

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