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Old 02-17-2013, 08:47 AM   #1
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GV90+ Multi-zone Installation


I recently replaced an older boiler with GV90+3 on an existing 3 zone system (2 heating and 1 domestic hot water). The zone valves are Taco 571s (3 wire). I have also replaced the 18ga 2 wire cable with 18 ga 3 wire cable and replaced the existing non-power stealing t-stats with programmable power stealing t-stats.

There are 3 sets of low voltage terminals coming off the GV90, i.e., (a) a pair of T-T wires (both black), (b) a pair of DHW wires (both blue) - connection to these bypasses the economy setting on the boiler, and (c) a set of R & C wires (red and black, respectively) for use to connect to power stealing t-stats.

I missed one instruction before I started up the boiler. On page 57 of the manual... http://www.weil-mclain.com/en/assets...ler_manual.pdf ... (wiring instructions are located on pp 55-58) it states that an isolation relay should be installed between the zone valves and the T-T terminals. I did not do this.

While the boiler appears to be functioning well, it does not recognize the t-stats and continues to provide heat regardless of the t-stat settings.

Any help with wiring advice would be appreciated.

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Old 02-17-2013, 10:47 AM   #2
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GV90+ Multi-zone Installation


First, are you using power stealing thermostats, or are you using thermostats that get 24 volts from the boiler's 24 volt transformer. Weil Mclain sometimes calls 24 volt thermostats power stealing, and they are not.

Would help if you posted the brand and model number of the thermostat.

Also if you wired to the Taco zone valves first, or to the thermostats first. Probably bleeding some voltage through the zone valve power head, and will need to add the isolation relay.

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Old 02-17-2013, 12:10 PM   #3
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GV90+ Multi-zone Installation


Thanks and Hello "beenthere",

The thermostat is a Honeywell RTH6580WF... here's the link: http://yourhome.honeywell.com/home/P.../RTH6580WF.htm

I wired to the zone valves first. Is that what you recommend or do you recommend going to the t-stats first?

Would you recommend any particular isolation relay? I am not sure what to use.

Also, would you recommend wiring the hot water zone directly to the DHW terminals or wire same as the heat zones, i.e., back through the T-T terminals?
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Old 02-17-2013, 12:16 PM   #4
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GV90+ Multi-zone Installation


Just an RBM relay is all you need, nothing special. Available at some HDs.
http://www.homedepot.com/webapp/wcs/...a#.USEdvKVm8aw

Should always go to the thermostat first. Then to terminal 1 on power head, then to common from power head terminal 2.

If the domestic is also on a Taco zone valve, get a second RBM relay for it.
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Old 02-17-2013, 12:40 PM   #5
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GV90+ Multi-zone Installation


Thanks for the quick reply "beenthere"

One last question... could I simplify all this by wiring through a Taco Zone Controller? I know it would be more expensive, but its for my own home and the diagnostics would be handy. In the case of the using the Taco Zone Controller I would not need the relay - correct?
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Old 02-17-2013, 01:50 PM   #6
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GV90+ Multi-zone Installation


Most zone panels don't have a separate end switch for DWH, so the boiler won't go to higher temp on a DHW call.

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