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Vitodens DHW priority question

28W28W Member Posts: 141
If the radiator circulator is running and the DHW aquastat calls for heat, should the radiator circulator immediately turn off? Mine kept running for a while, so both circulators (DHW and radiator loop) were going simultaneously.

Comments

  • gennadygennady Member Posts: 681
    priority

    if you need priority, you need interlock heating relay RA889A-1001 with DHW relay RA889A-1001 as described on page 32 of 5368 828 v1.6 manual



    Installation and Service

    Instructions

    VITODENS 100-Wd

    5368 828 v1.6 11/2010

    for use by heating contractor
    Gennady Tsakh



    Absolute Mechanical Co. Inc.

    www.AbsoluteMechanicalCoInc.com
  • 28W28W Member Posts: 141
    Thanks

    I was under them impression that DHW priority was essential, but it looks like it is optional. 
  • ChrisChris Member Posts: 3,056
    edited September 2012
    Simple Way

    If you zoned with Zone valves and used an exp version Taco Zone Control wire the system pump as a system pump to the zone control, plug in the Taco PC600 card in the power port on the zone control. Make sure priority switch is on. Take the XX on the PC600 card to DHW on the Vitodens, then take the XX on the zone control to RT..
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • 28W28W Member Posts: 141
    edited September 2012
    Thanks

    My system has a single heating zone, so there are no zone valves (if that's what you meant).  It is not currently set up for DHW priority, but the installer said the Taco relays he used will support that.  If I understood him correctly, DHW priority can be switched on or off at the relay, but is currently off.  Perhaps I misunderstood.



    I'll see how it goes during the heating season.  It is a small house (heat loss 33,000 Btu) and the DHW demands are not unusually large, so we should be OK.   



    The installer mentioned one potential drawback of DHW priority.  If the DHW circulator breaks and can't supply heat to the DHW tank, the aquastat will keep calling for heat, and the DHW priority will keep the heat to the house off.  If you are out of town when this happens, you could have pipes freeze.
  • ChrisChris Member Posts: 3,056
    How Does

    The boiler know tomgo into high fire? What Taco Relay did he use?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • 28W28W Member Posts: 141
    Taco SR501

    Does the relay tell the boiler to high fire for DHW, or does the boiler have on board logic to do that? When the DHW calls for heat, should the boiler always be at maximum fire?
  • ChrisChris Member Posts: 3,056
    It Sure Should

    Boiler should go to high fire on a DHW call. Something is missing from the picture. You have 1 zone of heat and 1 zone for DHW. If you have 3 pumps, boiler, zone and DHW cannot be using a single zone relay. Boiler pump is wired to pump on boiler control, Heating pump relay to RT and DHW relay to DHW. Do you have 2 SR501's?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • 28W28W Member Posts: 141
    edited September 2012
    Yes

    Two SR501s. When the aqua stat calls for heat, the boiler's display indicates DHW (little faucet icon). The boiler initially fires at full input, then ramps down as the water temp approaches 176 degrees.  According to Viessmann, this is normal operation.
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