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Thread: Evohome cycle rate and other settings

  1. #1
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    Default Evohome cycle rate and other settings

    Hi all,

    I’m looking for advice on the settings in the attached screenshot. Is 3 cycles per hour with a minimum on time of 3 mins normal for a gas boiler?

    FB63698B-B385-41D0-913A-52B8C3F66673.jpg

    Thanks

  2. #2
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    Quote Originally Posted by garmcqui View Post
    Hi all,

    I’m looking for advice on the settings in the attached screenshot. Is 3 cycles per hour with a minimum on time of 3 mins normal for a gas boiler?

    FB63698B-B385-41D0-913A-52B8C3F66673.jpg

    Thanks
    For a gas boiler, I would set to 6 cycles per hour, 1 minute minimum.

  3. #3
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    Quote Originally Posted by kevinsmart View Post
    For a gas boiler, I would set to 6 cycles per hour, 1 minute minimum.
    Agreed, 6 cycles per hour is optimal for a gas boiler and this is also the default. I've tried 3 and 12 cycles per hour and both have different drawbacks for a gas boiler.

    I use a minimum on time of 1 minute as well - if you set the minimum on time too high you add a lot of "dead band" to low load control meaning that a significantly larger heat demand has to be generated by zones before the boiler will fire, this can result in rooms going significantly under temperature before the boiler finally wakes up and starts operating. I found this especially so with low heat demands for bedroom radiators in the night.

  4. #4
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    thanks both.

    And what say we for an old, 43kW, non-condensing oil boiler? (This is what my parents have).

  5. #5
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    Quote Originally Posted by garmcqui View Post
    thanks both.

    And what say we for an old, 43kW, non-condensing oil boiler? (This is what my parents have).
    Oil fired boilers should be 3 cycles per hour per Honeywell documentation. Not sure off hand what the recommended minimum on time would be but probably more than one minute. Anyone reading who has an oil fired boiler who can comment?

  6. #6
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    Bear in mind that the cycle rate applies to zone valves, as well as to the boiler. If your valves are controlled by TPI, then they will open and shut as many times each hour as your cycle rate. I have set my cycle rate to 3 per hour, not for anything to do with the boiler, but to reduce the wear and tear on my zone valves. While the zone is within the +/- 1.5oC band its valve will open and close in each 20 minute period (i.e. six operations per hour - it would have been 12 with the default setting). My valves take 60 seconds to open or close so that still means that they are moving for 10% of the time. So far, none of mine has worn out but I do worry that this TPI cycling is not good for their longevity.

    This was discussed in this thread earlier.

    I appreciate that I am in a minority on this forum in not using HR92s universally and instead relying on zoning of my house using zone valves. Most Evohome users have HR92s on all radiators and so lock their zone valves open. In that case, the TPI control affects only the boiler and what I have written above is irrelevant.

  7. #7
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    Quote Originally Posted by Edinburgh2000 View Post
    Bear in mind that the cycle rate applies to zone valves, as well as to the boiler. If your valves are controlled by TPI, then they will open and shut as many times each hour as your cycle rate. I have set my cycle rate to 3 per hour, not for anything to do with the boiler, but to reduce the wear and tear on my zone valves. While the zone is within the +/- 1.5oC band its valve will open and close in each 20 minute period (i.e. six operations per hour - it would have been 12 with the default setting). My valves take 60 seconds to open or close so that still means that they are moving for 10% of the time. So far, none of mine has worn out but I do worry that this TPI cycling is not good for their longevity.

    This was discussed in this thread earlier.

    I appreciate that I am in a minority on this forum in not using HR92s universally and instead relying on zoning of my house using zone valves. Most Evohome users have HR92s on all radiators and so lock their zone valves open. In that case, the TPI control affects only the boiler and what I have written above is irrelevant.
    This is also true when using OpenTherm, so in that instance the Cycle Rate and Min On time parameters DO NOT affect the Boiler control, but only affect all the other relays in the system. It's quite strange that Honeywell didn't allow different parameters to be set to the different valves, no matter how they may be used. So a zone valve, a boiler relay and even the main motorised zone relays all inherit the single common parameters set. It was the only thing that drove me back to look at the old HM80, because that can have it's own parameters, different from the relays.

  8. #8
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    I dont have those settings, is it because Im set up as Zone Valve rather a boiler ? If so is it possible to set the cycle rate in that set up.

    Many thanks,


    Fly

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    What's in your System Parameters screen inside the Installer settings menu?

  10. #10
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    Quote Originally Posted by bruce_miranda View Post
    What's in your System Parameters screen inside the Installer settings menu?
    This is what it shows.

    IMG_2091.jpg

    I have mo idea why its upside down, ots correct on laptop !!
    Attached Images Attached Images
    Last edited by Fly100; 3rd February 2021 at 10:58 PM.

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