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Thread: How to control secondary pump from Evohome

  1. #31
    Automated Home Ninja
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    Just to wrap this up, the VR40 has been installed and seems to work perfectly. Shame it required another add-on board, but at least it all works now. I've left a rad valve slightly open until my heating guy can come and install an ABV on the secondary circuit. Happy days.

  2. #32
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    And do both pumps run for the same length of time?

  3. #33
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    Yes, hence why I really need a bypass on the secondary side. Really, it's no bad thing as the primary loop is scarcely 3 ft long, so not really enough to dissipate any significant heat on the overrun.

  4. #34
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    Sorry for reviving this thread, but did you fit an ABV on your secondary side?

    I'm having a LLH installed and all of the installers have said I can do away with the ABV, but I'm thinking ahead to installing HR92s on all my rads, in which case is it possible for all of the TRVs to be closed, yet the boiler still firing? The difference in my case will be that the secondary pump will be driven from the zone valve on the secondary side. Not knowing how evohome works, is there any scenario where all of the HR92s are closed, but the zone valve is still open? Or is that impossible?

  5. #35
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    Hot water demand.

  6. #36
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    DHW has its own zone valve - my system is S Plan plus.

  7. #37
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    Yes there is. It seems odd to me, but when closing down, Evohome shuts the HR92 valves before it shuts off the zone valves, boiler, etc. Plus there’s always the scenario of missing radio messages. You need a bypass of some sort. Period.

  8. #38
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by dty View Post
    Yes there is. It seems odd to me, but when closing down, Evohome shuts the HR92 valves before it shuts off the zone valves, boiler, etc.
    It's because of the way the system works. Heat demand comes from the HR92s. So when a zone is hot enough the HR92s shut down, then tell the controller that there's no demand. The controller then adjusts the heat demand (which can be anywhere between zero and 100 percent) that it sends to the boiler controls (BDR or OT).

    P.

  9. #39
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    Quote Originally Posted by dty View Post
    Yes there is. It seems odd to me, but when closing down, Evohome shuts the HR92 valves before it shuts off the zone valves, boiler, etc. Plus there’s always the scenario of missing radio messages. You need a bypass of some sort. Period.
    I thought this may be the case. Obviously, with a LLH, the boiler has a pathway to expel it's heat, but I was thinking about the pump on the secondary side not having anywhere to pump to, perhaps leading to premature failure. I'm loathed to install an ABV as they often seem to pass water when not intended, so am thinking perhaps a modulating pump is the answer.

  10. #40
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    My boiler is in the garage along with an open rad which acts as an overflow. Iíve also got 3 towel rails in bathrooms which arenít controlled by EH and therefore left partly open all the time.

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