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Thread: EvoHome Beta 02.00.19.31 - HW Priority Setting

  1. #31
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    Quote Originally Posted by bruce_miranda View Post
    What is the main reason why people still have a motorized valve on the CH loop, even when all the radiators have HRxx controllers on them? Is it just to stop the hot water rushing to radiators when the HW cycle kicks in?
    I have a heating zone valve in my S-Plan system (which I converted myself to S-Plan from gravity hot water - previously there were no zone valves) for a couple of reasons.

    1) Not all my radiators were HR92 controlled at the time. (But are now)
    2) A heating zone valve allows control of the average heat transfer through the CH circuit to be maintained during hot water reheat.

    When hot water is not reheating the boiler relay on my system TPI modulates the boiler to control average heat flow to the radiators. When hot water reheat activates the boiler relay goes to 100% resulting in the flow temperature reaching the set flow temperature (typically about 70C) and that would result in all the radiators going over temperature during a hot water reheat.

    However with a heating zone valve the intermittent opening of the valve during hot water reheat allows the average heat flow into the radiators to be roughly maintained so radiators do not go over temperature, but nor do they go cold like they would with hot water priority and a prolonged hot water reheat time...

    If you already have wired hot water priority and all radiators are HR92 controlled you won't see an advantage from a heating zone valve.

    But for those with hot water cylinders who do not want hot water priority (ahem) and/or don't have all radiators controlled by HR92's, a heating zone valve is desirable.
    Last edited by DBMandrake; 12th April 2020 at 05:22 PM.

  2. #32
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    Quote Originally Posted by bruce_miranda View Post
    What is the main reason why people still have a motorized valve on the CH loop, even when all the radiators have HRxx controllers on them? Is it just to stop the hot water rushing to radiators when the HW cycle kicks in?
    Funnily enough, and quite relevant to this conversation, my central heating zone valve failed just yesterday, discovered when I woke up to a cold house.... It's a Honeywell V4043 and is less than 3 years old which I installed myself. The motor has gone open circuit, so not terribly impressed by that given the price of the Honeywell valves vs others... hopefully the control head is still available separately so I can do a dry swap.

    As a workaround I have had to latch it into the fill position so effectively I have no heating zone valve now.

    And how does that affect the system performance ? As my custom wiring scheme kept the heating zone valve open continously when the pump was running and hot water was NOT heating, no change outside of hot water reheating, however the difference during hot water reheat is stark.

    I was sitting in the dining room just now at a comfortable 21C with the radiators cold (due to warm weather) and noticed the radiators creaking, went over to touch them and the previously cold radiators were now blasting at full heat, in the 10 minutes it took the hot water to reheat the room has now overshot to 22.5C and is uncomfortably hot. And I don't even boost the flow temperature for hot water reheat like some systems do.

    If the heating zone valve was working, in this low heat demand scenario it would have maintained a very low duty cycle (old firmware) or stayed off (beta firmware) and the radiators in the room would not have heated at all.

    So a heating zone valve is definitely beneficial in my scenario. My boiler is perfectly capable of getting radiators up to full temperature during a hot water reheat so this needs to be controlled by a heating zone valve to prevent rooms overshooting during hot water reheat.

    With the old firmware with TPI control of the heating zone valve during hot water reheat I did not experience overshoots related to hot water reheating.
    Last edited by DBMandrake; 17th April 2020 at 03:29 PM.

  3. #33
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    Quote Originally Posted by DBMandrake View Post
    Funnily enough, and quite relevant to this conversation, my central heating zone valve failed just yesterday, discovered when I woke up to a cold house.... It's a Honeywell V4043 and is less than 3 years old which I installed myself. The motor has gone open circuit, so not terribly impressed by that given the price of the Honeywell valves vs others... hopefully the control head is still available separately so I can do a dry swap.

    As a workaround I have had to latch it into the fill position so effectively I have no heating zone valve now.

    And how does that affect the system performance ? As my custom wiring scheme kept the heating zone valve open continously when the pump was running and hot water was NOT heating, no change outside of hot water reheating, however the difference during hot water reheat is stark.

    I was sitting in the dining room just now at a comfortable 21C with the radiators cold (due to warm weather) and noticed the radiators creaking, went over to touch them and the previously cold radiators were now blasting at full heat, in the 10 minutes it took the hot water to reheat the room has now overshot to 22.5C and is uncomfortably hot. And I don't even boost the flow temperature for hot water reheat like some systems do.

    If the heating zone valve was working, in this low heat demand scenario it would have maintained a very low duty cycle (old firmware) or stayed off (beta firmware) and the radiators in the room would not have heated at all.

    So a heating zone valve is definitely beneficial in my scenario. My boiler is perfectly capable of getting radiators up to full temperature during a hot water reheat so this needs to be controlled by a heating zone valve to prevent rooms overshooting during hot water reheat.

    With the old firmware with TPI control of the heating zone valve during hot water reheat I did not experience overshoots related to hot water reheating.
    Had a LOT of issues with Honeywell zone valves recently, to the point now going forward on new systems i'll be using Drayton.

    I'd just change the motor if you can, easy enough job to do and cheaper than buying a replacement top. If you do go down the replacement top road it's cheaper buying the complete valve and having a spare back than just buying a top.

    But goes to show Zone valves still have a place in some systems.

  4. #34
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    Quote Originally Posted by mtmcgavock View Post
    I'd just change the motor if you can, easy enough job to do and cheaper than buying a replacement top. If you do go down the replacement top road it's cheaper buying the complete valve and having a spare back than just buying a top.
    As you say a replacement head turns out to be more difficult to find and considerably more expensive than the whole thing (how pointless) so I ended up just ordering an entire valve for <£50 with free shipping, so I'll have a spare base left over.

    I did think about replacing the motor by itself and saw a couple available for around £15 but I wasn't sure exactly which one I'd need without further disassembly of the valve and as I'm in a hurry to get it fixed I didn't end up going that way in case I got the wrong motor.

    However as I'll have a new base left over I could actually get a motor later and repair the old head at my leisure leaving me with a complete working spare valve on hand for just another £15 for the next time one fails!
    But goes to show Zone valves still have a place in some systems.
    Absolutely.

    Just because an S-Plan system like mine has HR92's on all radiators doesn't mean a heating zone valve is useless. While it's true that the HR92's alone can stop radiators heating during hot water reheat when the heating is OFF, (HR92's fully closed) when the heating is ON but there is a low demand from the radiators, the minimal heat output of the radiators is maintained by a combination of HR92 valve restriction and low boiler/heating zone valve duty cycle...(primiarly the latter actually)

    If you then suddenly switch the boiler to 100% duty cycle (for hot water) for the same partial HR92 opening with no heating zone valve, the radiators will quickly get hot and overheat the room as happened in the situation I described.

    Hot water priority of course avoids this (but can allow radiators to cool instead) while my original system with both zone valves and the prior firmware means the TPI modulation of the heating zone valve keeps the radiators under control even during hot water reheating - they don't suddenly heat up, nor do they cool down, they really do stay about the same when hot water reheat kicks in, and I have never noticed any real change to radiator/room temperatures during hot water reheats prior to the valve failing.

  5. #35
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    Quote Originally Posted by DBMandrake View Post
    Hot water priority of course avoids this (but can allow radiators to cool instead) while my original system with both zone valves and the prior firmware means the TPI modulation of the heating zone valve keeps the radiators under control even during hot water reheating - they don't suddenly heat up, nor do they cool down, they really do stay about the same when hot water reheat kicks in, and I have never noticed any real change to radiator/room temperatures during hot water reheats prior to the valve failing.
    The issue with the HW priority i'm finding is that i've got a grumpy OH because her towels are no longer warm when getting out the shower Before we used to turn up the towel rails before jumping in the shower to warm your towel and dry them afterward. As it stands now in doing so doesn't give us a HW reheat cycle because of the bug, but when it does finally gets fixed means we won't get any heat in the Towel Rails till the HW is reheated - a good 25 minutes after you've finished the shower.

    She isn't very impressed at the minute

  6. #36
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    Quote Originally Posted by mtmcgavock View Post
    The issue with the HW priority i'm finding is that i've got a grumpy OH because her towels are no longer warm when getting out the shower Before we used to turn up the towel rails before jumping in the shower to warm your towel and dry them afterward. As it stands now in doing so doesn't give us a HW reheat cycle because of the bug, but when it does finally gets fixed means we won't get any heat in the Towel Rails till the HW is reheated - a good 25 minutes after you've finished the shower.

    She isn't very impressed at the minute
    One of the disadvantages of being a beta tester? So long as the final release allows HW priority to be an option, rather than compulsory, there should not be a problem.

  7. #37
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    Quote Originally Posted by CT1 View Post
    One of the disadvantages of being a beta tester? So long as the final release allows HW priority to be an option, rather than compulsory, there should not be a problem.
    I was more using as a point that the system does need to be able to be turned on/off - which at the current time isn't an option!

  8. #38
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    My valve is also a Honeywell and a couple of months back the HW did not heat up. It seemed that the valve had not tripped over to open up the HW circuit. Fortunately I cured it by manually moving the lever backwards and forwards a few times. Something must have caused it to stick. I am reluctant to get a spare in as a backup as when the lockdown is over the long awaited boiler and radiator replacement needs to be effected.

  9. #39
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    Quote Originally Posted by mtmcgavock View Post
    The issue with the HW priority i'm finding is that i've got a grumpy OH because her towels are no longer warm when getting out the shower Before we used to turn up the towel rails before jumping in the shower to warm your towel and dry them afterward. As it stands now in doing so doesn't give us a HW reheat cycle because of the bug, but when it does finally gets fixed means we won't get any heat in the Towel Rails till the HW is reheated - a good 25 minutes after you've finished the shower.

    She isn't very impressed at the minute
    Yep, got exactly the same complaint here, but with the bath, (shower is electric) she started running a bath, turned up the radiator before getting in the bath and at the end of the bath cold radiator and towels thanks to hot water priority as the reheat time after filling a bath is about 30 minutes. It was an "interesting" conversation to have to confess that no, the heating isn't broken, it's just running beta software on the Heating controller as that had previously slipped under the radar...

    If the final release of the software doesn't include an option to disable hot water priority I'm going to be forced to remove hot water control from Evohome and install a standard timer to keep harmony in the house! On the plus side it would solve my still ongoing CS92A "comms problems", so there is that I guess....
    Last edited by DBMandrake; 20th April 2020 at 08:39 AM.

  10. #40
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    Quote Originally Posted by CT1 View Post
    One of the disadvantages of being a beta tester? So long as the final release allows HW priority to be an option, rather than compulsory, there should not be a problem.
    Don't hold your breath. I think we'll either see forced hot water priority as it is now in the Beta, or they'll pull the feature entirely. I'm not holding much hope of seeing an on/off setting.

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