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  1. #1

    Dual zone thermostat control problems

    Hello I m running a hot water boiler with two zones in a multi-unit residential building. Zone one is in the original part of the building and zone two is in the newer addition. Each zone is managed by a separate thermostat connected to a separate zone circulator through a its relay. Once either thermostat asks for heat the the zone relay triggers and the zone circulator is activated followed by the boiler. Both thermostats can trigger concurrently with each circulator deactivating after its zone demands are met and boiler turning off after the last zone demand or its high limit is met. This is how it works most of the time. On occasion one thermostat will remain triggered well beyond it temperature setting causing its zone to heat up excessively. I have tested the voltage at the thermostat and the relay and determined that thermostat is indeed calling for heat and its not just the case of a sticky relay. I have replaced the thermostat and the problem persists intermittently. What to do?

    I should also mention that:
    reducing the temp on the thermostat during the problem turns the circulator and boiler off
    both thermostats share a transformer
    zone one is larger using a larger pump and cast iron rads
    zone two is smaller using a smaller pump and fin and tube baseboard
    there seems to be little separation in the piping between the zone (manual zone valves), not sure it this typical in a circulator zone management setup
    when one zone operates zone two heats up slightly

    I am considering getting a circulator controller like the Azel SP-82 to isolate the two zones completely if this is cause of the problem, a second transformer might be a cheaper alternative.

    Not sure how to resolve this problem, I can't have my boiler and circulator running endlessly. Any help is much appreciated.

  2. #2
    Join Date
    Nov 2004
    Location
    Skokie , IL near chicago
    Posts
    1,126

    Thumbs up Zone control problems

    hi Omega7 welcome to our clubhouse. First i'd like to know , are u running a 2 temp system for the different types of radiation? And do u have B&G flow control valves installed in the discharge lines of your zone pumps? Yes u should have separate xformer relays inst. for each pump . hope this helps, Rojacman

  3. #3
    Hi Rojacman, thanks for the response. I am not running a two temp system for the different rads. I don't have a set point controller or anything to compensate for outside temps either. i adjust the high limit as a set point a few times year. I was considering a Tekmar one boiler controller for this but that's probably overkill. Are there controllers out there that can change set point according which zone is requesting heat?

    There are only manual valves in the system which remain open. Beyond the lack of complete isolation between the zones, I suspect my problems may be related to poor thermostat placement as well. I going to try and resolve this first to see if it has some effect.
    Just to clarify I do have separate relays for each pump, I was just wondering if it mattered that both relays and thermostats are hooked up in parallel to the same transformer? Just to note the system has worked well with this exact configuration for a number of years.

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