Aquastat L7224U wiring to Taco 503-4

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Old 10-24-15, 04:07 AM
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Aquastat L7224U wiring to Taco 503-4

I just had a State SPX 50 DHPT installed in series with my tankless boiler. I currently have 2 zones off the boiler and I would like to cold start the boiler going forward to save fuel. I only want my boiler to run only when Thermostats call for heat. I am upgrading my aquastat from an old electromechanical to a Honeywell L7224U because I want to take advantage of the L7224U setting options (like LL, ASC and Circulator exercise). I also got cute and swapped out my old electromechanical relay and replaced it with the Taco 503-4. I have the wiring diagrams for both the Taco Relay 503-4 and the Honeywell L7224U to refer to. The question is how to wire the Taco Relay to the Aqaustat ? Do I bring the source 120vac to the Aquastat or do I bring the source 120vac to the Taco Relay ? I'm unsure if i should use the XX end switch from the Taco to TT on the aquastat ? Will I be able to use the Aquastat features for both zones ? Thanking you in advance for your professional assistance.
 
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Old 10-24-15, 09:09 AM
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Welcome to the forums.

You just installed a heatpump water heater and it's in series with your boiler. Why ?
 
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Old 10-24-15, 10:43 AM
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The boiler is in series with the SPX 50 heat pump hot water heater because it was easy to connect. The source water enters the boiler first then goes to the SPX 50 heat pump. The boiler does not need to run for 7 months out of the year so the water during the warmer months just passes through the boiler to the SPX 50 heat pump hot water heater. In my uneducated opinion the boiler now can be used cold start with the boiler only firing when the thermostats call.
 
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Old 10-24-15, 10:58 AM
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Check the water heater specs to see if they place a limit on the incoming water temperature... some do... never looked into the WHY of that, just know that some do.

You need to power BOTH the aquastat AND the Taco panel with 120VAC.

What I get from your post is that you have two zones with PUMPS and NO electric zone valves, is that correct?

What 'electromechanical' relays did you replace? 845 models?

The old aquastat was an 8124 model?

And both pumps are now wired to the 503 board along with their respective thermostats?

And there is NO pump wired to the 7224U ?

I need to fully understand what you have before advising any wiring...
 
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Old 10-24-15, 01:12 PM
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Hi NJT, Glad you picked up my posting. I have been reading these boards for awhile and you post lots of good information. My HL is set at 160' on the boiler Aquastat and I am aware of the incoming hot water concern. I have 2 zones with circulator pumps. I replaced an old R845A relay and a Honeywell 8124 control (good assumption). The Taco has the 120vac input points being fed off the boiler switch. From the Taco, zone 1 goes to the L7224U c1 & c2. Also, from the Taco, zone 2 goes directly to the Z2 circulator pump. In the L7224 C1 is being fed by the Taco zone 1, B1 goes to power vent and B2 serves as a common. The LED on my L7224U only displays information when the boiler is running, otherwise it is off ?
 
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Old 10-24-15, 04:35 PM
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The Taco has the 120vac input points being fed off the boiler switch.
That's fine.

From the Taco, zone 1 goes to the L7224U c1 & c2.
In the L7224 C1 is being fed by the Taco zone 1
No, this isn't right.

Since you've got the Taco panel, BOTH PUMPS will wire to the pump outputs of that.

Where do you have the pump for Zone 1 connected?

Also, from the Taco, zone 2 goes directly to the Z2 circulator pump
Correct.

B1 goes to power vent and B2 serves as a common
This part should be exactly the same as on the 8124.

The LED on my L7224U only displays information when the boiler is running, otherwise it is off ?
No, the display should be on whenever there is 120VAC power from the boiler switch to L1 and L2.

What do you have wired to L1 and L2 in the 7224 now?

The ISOLATED ENDSWITCH in the Taco goes to the T T terminals of the 7224.
 
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Old 10-24-15, 04:59 PM
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Oops. I misspoke when I said the L7224 is fed by Taco zone 1 on the C1 & C2. My L7224 points L1 & L2 are being fed off of my Taco Zone 1.
 
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Old 10-24-15, 06:24 PM
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My L7224 points L1 & L2 are being fed off of my Taco Zone 1.
No, that's wrong too.

You need L1 and L2 to be fed from the boiler switch, just as the Taco panel is.

Missed a question:

Where do you have the pump for Zone 1 connected?
 
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Old 10-24-15, 06:50 PM
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The zone 1 pump from taco is connected to the L7224 L1 & L2
 
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Old 10-24-15, 08:10 PM
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The zone 1 pump from taco is connected to the L7224 L1 & L2
Well... that's wrong.

You need to connect zone pump 1 to zone 1 output on the 503.

Connect zone pump 2 to zone 2 output on the 503.

Thermostats both go to the 503

120VAC from the boiler switch to L1 and L2 in the 7224 and to the AC input on the 503

Isolated endswitch on the 503 goes to the T T terminals in the 7224
 
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Old 10-25-15, 07:56 AM
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Hi, unless I am missing something,the easiest way to wire that, everything must go through the Taco 503-4 first i.e. thermostats,circulators,from that the End switch terminals go to TT on the L7224 which will have a 120 volt supply as well as a 120 volt supply to the 503,seems cut and dried to me.
Geo
 
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Old 10-25-15, 08:17 AM
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Yup, like the diagram in the manuals. There is no 'artistic license' allowed.
 
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Old 10-25-15, 08:43 AM
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One other thing,it appears that you plan on using the heat pump for deomestic hot water,correct?is there a pump somewhere that will circulator that water?
Just curious.
Geo
 
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Old 10-25-15, 08:59 AM
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Curiosity question. How does the L7224 control the circulators for my programmed setting ??
 
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Old 10-25-15, 09:21 AM
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How does the L7224 control the circulators for my programmed setting ??
It doesn't.

That's what the 503 is for. It alone controls the pumps.

When a thermostat calls for heat, the 503 starts the associated pump(s) and tell the boiler to fire up. In a pump zoned system with a pump control panel like the 503, all the 7224 has to do is to control the water temp in the boiler.
 
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Old 10-25-15, 09:22 AM
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it appears that you plan on using the heat pump for deomestic hot water,correct?is there a pump somewhere that will circulator that water?
Domestic water needs no pump... pressure comes from the water supply.

UNLESS one wants a 'hot water REcirc system, but that's a whole 'nother subject.
 
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Old 10-25-15, 10:36 AM
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Ok. That's unfortunate. I was hoping to use all those settings on the 7224, like the 5 day circulator exercising, anti short cycle
 
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Old 10-25-15, 12:01 PM
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Got it! I wasn't thinking of that,the Recirc is a good plan if the HW source is a distance from the useage point.
Geo
 
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Old 10-25-15, 05:06 PM
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was hoping to use all those settings on the 7224, like the 5 day circulator exercising, anti short cycle
Everything except the circ exercise should still work I think.
 
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Old 10-25-15, 06:50 PM
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NJT. Thank you for your guidance and the time you took to offer your expertise. The system is working as expected. Taco receives signal from therms and fires associated circulator. I am still interested in understanding how the 7224 works in regards to its programmed settings (there's a lot the 7224 offers) I'm trying to squeak out every bit of efficiency from this boiler.
 
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Old 10-25-15, 06:52 PM
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I am still interested in understanding how the 7224 works in regards to its programmed settings
Read the manual cover to cover... and then if you have any questions, feel free to ask!
 
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