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Thread: Adjusting the Boiler Cycle time? Boiler cycling every 10mins.

  1. #1
    Automated Home Jr Member
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    Default Adjusting the Boiler Cycle time? Boiler cycling every 10mins.

    At night we keep only our room & our young son's room on/monitored via the Radiator HR92s.

    In our bedroom the heat from the two of us generally keeps the room above the 18 degrees we set it at, but our son's room does need constant top ups throughout the night - most nights.

    This means the boiler is cycling on/off every 10 minutes for maybe 1 minute to boost the heat.

    I am concerned that our new Worcester Bosch boiler is going to suffer with this very regular cycling. I figured at 6 times an hour, for 10 hours for weeks on end is a *lot* of on/offs - something most appliances don't like.

    Should I be worried about this? Is it worth increasing the 10 minutes to 15mins and sacrificing some of the Evohome control for the sake of the boiler longevity?

    Cheers

  2. #2
    Automated Home Guru
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    I agree cycling like that is most likely to increase the probability of a failure. I'm wondering why it's cycling like that to maintain the temperature 1-min is hardly enough time to fire the boiler and get water to the radiator for the HR92 to respond and remove the demand. Try turning the temperature up a little in your son's room to see what that does maybe +0.5C? either that or increase the time to say 20-mins, I find being radical exposes the issue, so changing from 10 to 15 may not make much difference, but 10 to a much bigger value will, then you can always come down from that. I'm not sure why the system does this, it does not seem very efficient, but then cars tend to do this now in traffic with auto-stop/start.

  3. #3
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    Sounds like perfectly normal TPI behaviour to me for a single radiator running on low at night. I wouldn't be concerned - all modern boilers are designed to cope with TPI control.

    If you have a 23kW boiler that is only trying to warm a single radiator its no surprise that it will modulate down to a 10% duty cycle!

  4. #4
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    Thanks for the replies guys.

    It's a 30kw boiler, but it's a reasonable sized 4 bed detached modern house, over spec'd by an easy 15% I'd say (something I regret doing now, but all plumbers quoting advised at the time) .

    All rads/UFH loops are controlled except for bathrooms/toilet (on standard TRVS) and the hallway/corridor rads.

    All get warm alongside son's bedroom, but I'm OK with this to keep some chill off they house.

    Googling has failed to show me how to adjust the TPI up from 10mins? The manuals have annoyingly gone walkabouts. Can anyone advise me briefly? Thanks

  5. #5
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    Hold down Settings for 10 seconds for the installation menu, then go into System Parameters.

    Change cycle rate from 6 to 3 to increase the cycle period to 20 minutes. You can also adjust minimum on time to increase it from the default of 1.

    Unless you have special circumstances the default values should be fine though.

  6. #6
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    Thanks for that, holding it down for 10 seconds gives me the system configuration menu after 3 seconds, and system parameters only gives options for the internal sensor offers and stored hot water?

  7. #7
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    Ah ok.

    If you are using an S-plan or Y-plan configuration with only two BDR91's you can't adjust the cycle rate or minimum on time.

    Only if you have a 3rd BDR91 acting as a boiler control relay or you don't use hot water control at all. (1x BDR91)

  8. #8
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    Damn, OK yeah I have a S plan with 2 motorised valves operating hot water and heating.

    It a standard pressurised system, with megaflow cylinder.

    Boiler was installed last year alongside the evohome kit. Got 4 more years of warranty left, but it turning on and off 6 times an hour all night does have me spooked slightly.

    That being said, most evohome users must have a similar setup with similar switching at night during cold spells?

  9. #9
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    Worth adding, the system does work perfectly well as is. It keeps both our room and son's room at bang on 18 degrees no matter how cold it is. Including our room being slower to cool down with wife/my body heat compared to sons.

  10. #10
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    Well I have a 24 something year old boiler that has been switching on and off every 10 minutes for the last year on Evohome without problems...

    Of course if there is no demand at all the relay will stay off and if there is a "full" demand (at least one zone is 1.5 degrees or more below it's set point) then the relay will stay on permanently, but with any partial demand (all active zones are with +/- 1.5 degrees of their set points) it will switch on and off once in every 10 minute cycle - the only difference is what proportion of the 10 minutes is on and what is off, the number of switches per hour stays the same. (Hence the cycle rate setting - which is fixed at 6 times per hour on a two relay configuration)

    We have the master bedroom scheduled to about 16 degrees through the night which is a bit higher than we used to have it, but we now have a 7 month old sharing the room with us and too much less than 16 and he will sometimes wake up in the night. The room is scheduled to 18 from 9pm to 11pm to get the room warmed up for bed time so typically once it drops to 16 at 11pm the boiler will go off and won't come back on again until some time in the night - depending on how quickly the room temperature drops to 16 based on outside conditions.

    Sometimes it doesn't happen until as late as 3am when it will come on at a low duty cycle and get the radiator just warm enough to keep the room steady at 16. Other rooms in the house are scheduled to 5 at night which is essentially off, and I do not have any bypass or uncontrolled radiators - so when the bedroom is the only room scheduled to be on at night, none of the other radiators in the house will inadvertently heat up, and that's the way I like it.

    The temperature control in the bedroom is really spot on through the night, although we did find that a remote wall mounted sensor near the head of the bed was necessary for best results as the HR92 under the window would detect cold air coming in a slightly open window and bring the radiator on when it didn't need to, which the wall sensor solved.

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