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Old 10-02-2011, 10:09 PM   #1
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Hydronic heating problem


I have an oil-fired boiler with four zones. Originally, it was a Honeywell aquastat plus three Honeywell 845A relays for the other three zones. The relay in the aquastat failed, but instead of replacing the aquastat I added another 845A at the end of the "chain" to make it easier. Now my problem is that when the thermostat calls for heat, nothing happens unless another zone also calls for heat. All the other zones work fine by themselves, and when they call for heat the problem zone doesn't run. Does anyone have a clue where I may have miswired it?
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Old 10-03-2011, 12:37 PM   #2
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Hydronic heating problem


the 24Vs for that last zone is waiting for a closure from one of the other 3 it seems for its 24V remove the last zone R wire from the run from its stat and catch a constant 24Vs.the 24V hot "R" should go up to the stat then back down to the control valve.the valves have 2 wires each the C side should be one wire nut back to the TR the hot Rs can be wire nuttend also but go up thru the stat then down to the valve.might of wired the last one thru an end switch if you have 4 wires per valve
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Old 10-03-2011, 01:37 PM   #3
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Hydronic heating problem


Sorry, I should have said that I have one Taco 1/25HP circulator (probably 007) per zone, not zone valves.
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Old 10-03-2011, 02:49 PM   #4
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Hydronic heating problem


Ok your still controlling a relay with a 24V coil from the stat then that runs the circ pump dedicated to its zone.....all the zone circ relays should all be wired the same to that R from the stat and to the C from the TR.do you have a seperate TR for the zone controls away from the actual boiler controls
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Old 10-04-2011, 02:51 PM   #5
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Hydronic heating problem


I believe my circulator is hooked up to terminals 2 and 6. Terminal 2 is also hooked up to the common of the line power. The line hot is connected to terminal 3, which is jumpered over to 5. Terminals 1 and 4 should be hooked up to 1 and 4 from the last relay in the line (which ultimately ends up at ZC and ZP.

I'm guessing one of these became disconnected such that the circuit is broken unless something energizes ZP. Or, maybe reversing the polarity matters?

I'm going to pull the cover to confirm all of this when I get home.
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Old 11-07-2011, 09:02 AM   #6
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Hydronic heating problem


Finally got around to checking my connections. Everything was wired up as expected. I made sure to check for loose connections and shorts. This time, I also got out my multimeter to check voltage and continuity. There's 120V across 2 and 3 (and, of course, 5). However, there is not 24V across the thermostat terminals unless another relay is engaged! So I've found the problem, but I don't know how to fix it.
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Old 11-07-2011, 09:26 AM   #7
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Hydronic heating problem


I should probably also point out that I did remove the Honeywell digital setback thermostat and test with the old "round" one that it replaced to make sure the thermostat wasn't causing a problem.
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Old 11-11-2011, 12:40 PM   #8
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Hydronic heating problem


There appears to have been a break in one of the wires on terminals 1/4, which come from the ZC/ZR on the aquastat. I replaced the wires and all is well.
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