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changing Indirect H/W Boiler to Cold start

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Robert_H
Robert_H Member Posts: 305
in Oil Heating

I recently had to replace a boiler aquastat, I replaced it with a Honeywell L7224U1002. The system has an indirect but is set up as a warm start boiler. So I want to switch over to a cold start operation. However, I can't yet because of the wiring of the indirect circulator and indirect Aquastat.
This is a small home that heats primarily with their mini split system so even in the winter time it doesn't make sense for this boiler to always be warm.  Tt definitely doesn't during the summer. 
The the system has single zone valve (it was once a two zone system but one zone has been removed) and a circulator that feeds the zone valve and then independently, a circulator that feeds the the indirect and does not use its own zone valve. The aquastat on the indirect provides L1 to the indirect circulator.
So the boiler is set up as a warm start because there's no call for heat when the indirect needs heat from the boiler. I'm thinking I need to add a switching relay and stop powering the indirect circulator through indirect Aquastat. Is there a simpler "less costly to the homeowner" way to do this. I'm also seeing the single zone valve as useless and just something to break in the middle of the night.

Thanks

Robert

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 20,172

    You want the temp control on the indirect to start the indirect circulator and start the boiler.

    You want the heating thermostat to start the heating circ and fire the boiler (or the thermostat opens the zone valve and the zone valve end switch pulls in a relay to start the boiler and the heating circ)

    2 Honeywell RA832A relays would do it.

    You only need an aquastat for a high limit. An L4006A would do that.

    There are numerous other controls you could use.

    Robert_H
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,173
    edited 1:50AM

    You replaced a L8148 with a L7224U. is that what you are talking about?

    OR

    You replaced a L8124 for a tankless coil boiler with a L7224U and installed the indirect and want to convert to a cold start boiler. That is a little different.

    In either case you don't need the burner to keep a minimum temperature. The L7224U can do that by setting the Low Limit to the lowest temperature then one more click past that low temperature. The temperature display will read OFF . The L7224U will no longer operate the burner unless there is a call for heat at TT on the L7224U, or you get external 120 VAC input to the ZR on the L7224U from the DHW thermostat.

    How is your DHW indirect tank getting hot water from the boiler? …a zone valve or a circulator pump?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,173
    edited 2:53AM

    When there is more than one circulator that can operate the boiler, there needs to be a Flow Control device to prevent the water from the zone that is not operatinf from getting flow backweards from the circulator that is operating the other zone. In this diagram the space heating pump is operating and the water is flowing backwards thru the water heater loop.

    image.png

    Think about what will happen in the summer when the boiler operates for DHW and the space heating loops get heat flowing backwards thru the loop.

    Depending on what circulators you have you may be able to add the flow check with a small IFC device added to the existing circulator pump. Depending on the condition of the zone valves you ca nwire them to be the valve that prevents flow when there is no call for heat from the space heating zone and the DHW zone is calling for heat.

    I would need to know more about what is already there to tell you how to do this,

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,173
    edited 3:58AM

    For the DHW part of the control system, that is easy, You need to get one switching relay like the Taco SR501 or the Resideo R845A. The L7224U for the boiler gets the space thermostat to R and W and the heating circulator connected to C1 and C2. The thermostat and circulator for the DHW gets connected to the switching relay. The contacts from the 5 and 6NO connect to the ZR and the L1 on the L7224U (shown in red). This will power the burner thru the high limit, without powering the space heat circulator.

    image.png

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

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