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Thread: Atag IS24 Plus Evohome Plus Opentherm

  1. #41
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    Quote Originally Posted by Edinburgh2000 View Post
    Because in the first hour of a winter's morning Loop is showing 65kW in each of the four quarter-hours. And thereafter - being something of an anorak - I can watch the boiler and all the zone valve controls and see that all zones are still demanding heat (i.e. no TPI demand reduction) but the power output of the boiler drops because the CH output temperature has reached the set point (70oC in my case). The boiler only switches off when the outlet temperature goes six degrees above the set point. That rarely happens.
    Ah, so Loop data + watching it. I thought I was missing a trick somewhere.

  2. #42
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    Out of interest, does anyone have a simple explanation of how a modern condensing boiler should work? I ask because what I am seeing, with HW demand OFF, is the boiler slowly cranking up to max flow temperature. As zones reach their set points, the flow temp remains the same but the pump speed reduces markedly and the boiler is audibly much quieter indicating, to me, less heating output.

  3. #43
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    My water pump speed changes but only because I have an external 'modulating' pump that reduces based on flow resistance (pressure) as radiators turn off. This is not in any way controlled by evoHome. My boiler becomes quieter as it modulates down because the fan speed drops which correspondingly uses less gas and the burn is less intense. I can monitor my fan speed and gas flow in realtime over IP so I see the reductions and then the start / stop cycling and can graph it.

    @Edinburgh2000 I'm envious of your modulation down to 14KW - that's nearly 5:1 - mine coincidently is a Potterton EC65 on just over 2:1 (from memory - will check)

    PS Actually if I use the original thermostat with my boiler - as it approaches set point it nicely lowers and maintains flow temp at about 40 degrees - via evoHome when it fires it tends to go to max and have to modulate down immediately and then switch off quickly (as only a couple of zones need a bit of heat) flow temp is a short 'max' temp which causes overshoots in cast iron rads.
    Last edited by Kevin; 12th April 2017 at 08:59 PM.

  4. #44
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    Your home sounds very similar to mine (sealed S plan with unvented tank and heat only boiler). I've been going through the same procrastinations and seriously considering Atag.

    What made you go for the system boiler? Or did you have a system boiler previously? I'm currently heat only, but could convert to system when I upgrade.

  5. #45
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    Quote Originally Posted by fergie View Post
    Your home sounds very similar to mine (sealed S plan with unvented tank and heat only boiler). I've been going through the same procrastinations and seriously considering Atag.

    What made you go for the system boiler? Or did you have a system boiler previously? I'm currently heat only, but could convert to system when I upgrade.
    I have a 19 radiator/5 bed home with an unvented 250L OSO cylinder. The IS24 has replaced an Ideal Classic system boiler.

    I am still trying to get my mind around Opentherm and condensing boilers. At the moment, about 50% of the house is calling off and on for heat. The boiler currently has a flow temperature of 60C and a return temperature of 54C. There are considerably less zone temperature variations than was the case; no boiler cycling and the boiler itself is whisper quiet.

    Edit: I have just checked. Three zones and 10 radiators all at set temperature. The boiler has flow/return of 50C/49C. Pretty clever stuff.
    Last edited by HenGus; 13th April 2017 at 05:47 PM.

  6. #46
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    I'm about 16 rads + unvented cylinder. I'm currently running evohome with 12 valves and not connected to the current glowworm boiler at all. I'm hoping to go OT once I get a new boiler sorted.

    I'll drop you a pm.

  7. #47
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    HenGus,

    I have been watching your progress with the Atag with interest after my own wrong boiler choice last year (Worcester Bosch 24RI - noise and vibration issues causing no sleep in nearby bedroom).
    I may replace the WB with a OT type boiler now.
    If you had your time again would you advise on going for the Atag again?
    Is there an installer you would recommend? (I am as my moniker suggests in Amersham, Bucks).
    I run Evohome with UFH (ground floor), Rads (1st and 2nd floors) and two Megaflo tanks in a larger recent build 5 bed property with high insulation and all with differing heat timing requirements, so mostly no multiple heat loads being called for at the same time.

  8. #48
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    Quote Originally Posted by Sean in Amersham View Post
    HenGus,

    I have been watching your progress with the Atag with interest after my own wrong boiler choice last year (Worcester Bosch 24RI - noise and vibration issues causing no sleep in nearby bedroom).
    I may replace the WB with a OT type boiler now.
    If you had your time again would you advise on going for the Atag again?
    Is there an installer you would recommend? (I am as my moniker suggests in Amersham, Bucks).
    I run Evohome with UFH (ground floor), Rads (1st and 2nd floors) and two Megaflo tanks in a larger recent build 5 bed property with high insulation and all with differing heat timing requirements, so mostly no multiple heat loads being called for at the same time.
    That's a difficult one to answer as the new boiler has been installed for less than a month. That said, I have no regrets so far. The boiler is whisper quiet in operation and the set up with my existing Evohome system was nothing more complicated than deleting the existing heating BDR from the Controller (unbinding the BDR just to be doubly sure) and then setting up the OT bridge as a boiler relay.

    I used an Atag recommended installer and the boiler warranty has been increased to 10 years at no additional cost to me. My installer insisted on a full water flush which, with 19 radiators, took most of a day. Throughout the flushing process, he took repeated water PH, Fe and ionisation samples and the system has been installed to comply with the latest German Standards on CH systems without any inhibitor. The system is protected from rusting etc with a SpiroVent Microbubble De-aerator and SpiroTrap Dirt Separator. The logic behind this is that clean water without the presence of air cannot cause rust, whereas a system with too much/too little inhibitor can. Interestingly, on the afternoon of the flush, I had three other CH installers visit all armed with their brand new ( and very expensive ) water testing kits getting some hands-on onsite training from my installer.

    Why Atag? Firstly, in the Netherlands, Opentherm for new systems is the norm. That said, I was aware from this forum that others were using Valliant, Ideal and Viessmann with Opentherm. Various posts on this forum, and others, pointed out some of the issues. I won't repeat them all here. I found myself leaning towards the Intergas RF Eco. It is listed as fully compatible with Opentherm but it was only after I chatted to an Intergas installer on another forum that I found out that it has problems coping with multiple zones. I am still not sure why this is the case, as Honeywell has since told me that, for Opentherm control purposes, Evohome acts as a single zone (albeit, one with many inputs). That, left me with the Atag.

    I contacted Atag and they provided me with a list of their approved installers. I then had a chat with their technical department and they pointed me in the direction of an installer in Dursley, Gloucs. I suggest that you give Atag Technical Support a ring, If no joy, then PM me and I will give you my installer's details.

  9. #49
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    A very useful reply, thank you. I have already contacted Atag UK and am waiting for their response. I am also waiting for Worcester Bosch UK and their installation engineers to reply to me but now the boiler is installed and some 9 months old they seem in no hurry to come back to me at this time.

  10. #50
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    I don't under stand the logic of the Spirovent to prevent corrosion . I understood (perhaps incorrectly) the corrosion is mostly by dissolved oxygen not by free air , Spirovent cannot remove dissolved oxygen. Also an inhibitor like Sentinel X100 can be dosed to excess without negative impact. For me an inhibitor would always make sense.

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