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Setting up a Taco Post Purge Timer

WrenchWrench Member Posts: 17
Would like to install a Taco PC-600 post purge timer into a Taco SR504EXP zone control box with the intent on allowing the circulators to run for a set time after the call for heat shuts the system down. The post purge feature is built into the Burnham ESC boiler being used, but was disabled by design when the zone control box was utilized.

I see in the instructions the card apparently only controls the priority zone.

Link to PDF instructions:

Even though it's a four zone control, the system is set up with two zones and since there is no indirect hot water (domestic hot water is still from an old tank) the priority zone is not active.

Will this card post purge any of the heating circulating pumps, and if so how should it be set up?


  • Paul48Paul48 Member Posts: 4,492
    Let the boiler control one circ and its post-purge, and let the sr504 control the other.
  • icesailoricesailor Member Posts: 7,265

    "" Even though it's a four zone control, the system is set up with two zones and since there is no indirect hot water (domestic hot water is still from an old tank) the priority zone is not active. ""

    Are you saying that there is no indirect water heater with boiler piping feeding a coil? But is it a hot water storage tank that is being piped through an internal tankless heater on the boiler? If this is so, they are not usually connected through any Taco SR-50* relay. The boiler is set to operate at whatever you set the operating/Low Limit control and when the boiler water gets below that setting, the burner starts.

    If you only have two zones, and one zone is large, the other is small, and you can make the "priority" zone work with the Post Purge on the Burnham, can you make the largest zone the priority zone? At least to try? Just move the wires in the SR-50* to the priority zone.
  • WrenchWrench Member Posts: 17
    Domestic hot water is not connected to this boiler at all.

    Are you suggesting I connect the circulator(s) white leads (neutral) via the 504 and the black leads (hot) through the boiler? Can't fathom that without a schematic!

    Is there a way to have this card simply post purge preferably both circulators via the 504 control box?
  • Joe MattielloJoe Mattiello Member Posts: 589
    The PC 600 was designed for use with an indirect water heater. The objective is to take the residual heat from the boiler and continue heating DHW after it's satisfied. There is a small window of opportunity to accomplish that before the boiler temperature drops below the water heater temperature, and if you allow the circulator to operate past that threshold you will begin taking heat out of the tank using the colder boiler as a sink. This of course would be more prevalent in the summer, when you're not using the boiler for HVAC.

    If you do not have a water heater on the priority zone, you can use the post purge feature to continue heating a particular area of your home. the PC600 wont mind:-)
    For your reference I attached the instruction sheet. I had a copy stored on my hard drive. Our IT department always complains about me storing too much stuff, but how do you pick and shoes what to lose. Keep it all, someday Dan H may want to write another book, and want access to my archive.
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • WrenchWrench Member Posts: 17
    Thank you for the comprehensive answer. The boiler has no function related to domestic hot water, the 504EXP is capable of four zones but only two for baseboard heat are utilized.

    How can I best utilize the card to power the circulator(s) for a few minutes after the thermostat is satisfied?

    It's all connected to a Burnham ESC boiler which has a now capped yellow wire which would have provided pump over run, but that ability was lost when the 504EXP was integrated. The underlying intent is partially to force the boilers standby temperature to decrease as it has a habit of short cycling and having the pumps run a few minutes post cycle would address that by encouraging it to run longer because of the colder start temperature.

    It's description makes it seem perfect for this need:

    Description for Taco PC600
    You can use Taco's exclusive Plug-In PowerPort Cards with any Taco Expandable Control (-EXP models) to enhance total system integration and performance. Each Taco Expandable Relay comes standard with three PowerPort slots to accept any combination of cards. By controlling the operation of the circulators attached to the switching relay, PC600 cards are an ideal way for you to provide energy savings, system protection and an increased comfort level.

    There are no complex controls to wire+just plug the cards into any of the slots provided. Mix and match PowerPort Cards for post purge, priority protection and universal timer/pump exercise to quickly customize any system. You can also use PC600 cards without additional wiring in parallel with Taco Add-on Power Controls to add even greater system control and boiler optimization.


    Solid-State Electronic Cards Use with any Taco Expandable Relay (-EXP models)
    Simply Plug Into Any One of Three Slots No Wiring Required
    LED Lights
    Fixed and Adjustable Time Delays
  • Joe MattielloJoe Mattiello Member Posts: 589
    edited September 2014
    The PC600 works exclusively with the priority zone, so your zone 4 will enjoy priority, and post purge.

    To reiterate, the control will work the same, regardless of what your using the zone for. The caveat is, priority switch needs to be set to on, so the control recognizes DHW which is what the PC600 card was intended for, and purge the boiler when using PC600. I hope this addresses your concerns. Please advise if you have additional questions.
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
  • WrenchWrench Member Posts: 17
    Not what was expected, but better than nothing. I will move the leads for the most used zone to the priority terminals as instructed and enjoy post purge benefits on that zone (hopefully).

    The Burnham ESC boiler does have an unused yellow lead in the junction box intended to provide the hot lead to a circulator, which I believe may also provide an adjustable post purge function. But I have no idea how to utilize it with the 504EXP board or to independently control the second zone.

    What would you suggest to implement post purge on the second zone?

    Thank you!

  • WrenchWrench Member Posts: 17
    edited October 2014
    I don't see an edit, so am adding this as a follow up question.

    As I look into it, incorporating priority for one baseboard heating zone would not allow the other baseboard zone to run while it was calling for heat... is that correct?

    If so, the 600 would not be a good control for implementing within a two zone heating system as oftentimes both zones run simultaneously. Will the card be responsive at all with the priority zone turned off?

    Is there any way to utilize the card to any benefit and have the control responsive to two zones?

    (found the edit, sorry for double posting)
  • WrenchWrench Member Posts: 17
    Have been looking at this install manual thinking there's gotta be a way of doing this.,d.aWw

    The ESC boiler provides post purge through the yellow wire.

    Our system does not have any DHW connections. It does have two thermostats and two Taco 007 pumps.

    How can I utilize both the SR504EXP with the purge timer card and the boiler control shown in the link to gain post purge on both pumps?
  • Paul48Paul48 Member Posts: 4,492
    You may not need the sr504 at all. I can't tell from those instructions, whether the DHW/ ZONE circ would also have a post purge. You'll have to check your parameters. If so, the 504 can go on the buy,sell, barter page.
  • WrenchWrench Member Posts: 17
    With the PC600 card in place:

    Priority zone turned off with thermostat calling for heat switches the boiler on for a moment then off, and the card purges the pump. Other zones are operative.

    Priority zone turned on with thermostat calling for heat switches the boiler on for a cycle and the card purges the pump. Perfect, but other zones are not operative.

    So the card, as I was told, isn't going to purge the heating zones as expected.

    I was thinking of running the now capped hot yellow wire from the boiler, which provides power to the circulator and post purge of up to 10 minutes, to the 504 box and piggybacking it onto the hot wire of one of the circulators. I could wire it with a relay which would give zone 1 the desired post purge, and when the zone 2 is active would post purge into zone 1.

    Less than ideal, but as a means of making the boiler have a colder start for a longer cycle mission accomplished.

    Might there be a more effective way?

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