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Thread: Evohome Bug

  1. #41
    Automated Home Ninja Dan_Robinson's Avatar
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    With the TPi thermostat, are you still only sending heat to one radiator? Or is the rest of the system accepting heat from the boiler?

    What make and model boiler is it? What output? What is the heat loss of the room and the size of the radiator?

  2. #42
    Automated Home Jr Member
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    1 radiator only working. Please see if you get the temperature oscillations I get.

  3. #43
    Automated Home Ninja Dan_Robinson's Avatar
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    ???? Can you elucidate?

  4. #44
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    I think what Mikey's trying to say is that Honeywell should test with just 1 radiator to be easier able to re-produce his/mine issue.

    Quote Originally Posted by Dan_Robinson View Post
    With the TPi thermostat, are you still only sending heat to one radiator? Or is the rest of the system accepting heat from the boiler?
    the former. It's actually 2 radiators, the ones in the living room.

    What make and model boiler is it? What output? What is the heat loss of the room and the size of the radiator?
    Vaillant VHR24-28C from about 2000. I think it's about 22KW and able to modulate to about 50%. I have the max water temperature set to 60 instead of the default 90 to save gas. It should mean less KW's going into the radiators as well. The living room radiators are about 4KW combined. I've got no idea about the heat loss. The house is from the '30s with big windows, so there's certainly loss. But it's between 2 other houses and the glass is insulated. So it's not awful... It's really all pretty standard set-up when compared to other comparable houses and their radiators/boilers.

    And: other thermostats work just fine. We've tried with a really really old mercury-filled one from honeywell and a slightly newer Honeywell Round (wired, with TPI, using the same 10 minute cycles as Evohome). The BIG difference I noticed between Evohome and Honeywell Round in on/off behavior is that I NEVER saw the BDR91 every skipping a 10 minute cycle, untill at least 0.7 above setpoint (after wich it would finally stop further heating the room, and stay totally OFF for at least 2 hours, radiators becoming totally cold, the living room cooling down a full degree very uncomfortable, etc). And trust me, I've spent a lot of time monitoring that thing. Once the BDR91 turned ON once, it would continue to turn ON for the minimum run time every 10 minutes, untill the living room finally being way above setpoint. This heating up process would often take at least 1.5 hours. So the Evohome system should have plenty of time to react to this situation, but just didn't. The Honeywell Round however would skip a 10 minute cycle pretty often when the desired temperature was (about to be) reached and no additional heat was needed. So to me it's really no wonder that the Round was doing a much better job at maintaining a constant temperature. I think the BDR91 algorithm is missing a cycle-skip-part. If for example it receives only a 10% heat demand, it will still go ON for the minimum run time every 10 minute cycle. It only stays totally off when it receives a 0% demand. However, Evotouch does not seem to send a 0% demand, unless the room is probably at least 1 above setpoint.
    Last edited by erik; 28th October 2015 at 07:57 PM.

  5. #45
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    PS: I'm using Tado now and it keeps the room at 1 temperature just fine as well. Very steady graph from my temperature logger. Now just have to wait untill next year, when they'll release their smart radiator heads for zoning.

    @Dan: I gave you the info you asked for. Is there anything you can conclude from it?

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