24Vac from Honeywell 7224 for wifi thermostat's c wire
Hi all,
My home has a Honeywell L7224 aquastat controller (manual) which is connected to a couple of two-wire Hunter battery-operated thermostats, which I am looking to replacing with Honeywell RTH9585WF Smart Thermostat (wifi) which require a C wire. At my skill level I can run wires so I'm not concerned about that.
Unfortunately the L7224 doesn't have a obvious C wire connection but I found an old but promising thread here, Wiring a new Honeywell Thermostat to Honeywell Aquastat Controller in which @PJmax suggested that there may be 24Vac between terminals marked T and 2 in the schematic. I measured this yesterday and I measure ~27Vac across those terminals, and ~13Vac between T and 1.
My question: can I connect the C wire to terminal 2 of this aquastat and pull it up to the thermostat?
Secondly, I have another zone in the basement, and also a hot water heater connected to this aquastat. How would I handle the second thermostat?
Here is photo of DH zone control panel mentioned in Post #7 showing easy to see wiring. No zones were active so only LED for 24 volt power was lit.
White page on upper left List 4 step to activate zone and basic color coded wiring for all zones. Labels on right side on have blue tape for thermostats across top and yellow tape wire for zone valves on bottom. Terminal blocks with screw make wiring and changes easy.
Panel is protected by removeable Plexiglass plastic sheet.
A second text sheet, out of picture, at bottom explains color codes and physical location of zone vales.
Bring all zone wiring to central panel makes life easier for both DH and future repair person. Post this hoping it will make it easier for others.
Modern thermostat use very little power for their electronics. The heating contacts, RH and W usually rated at 3 amps, far less than most heater T T controls draw.
How much spare power the L7442 has for other things, i.e. zone valve is another issue.
To simplify things am using one 24 volt 75 VA transformer for everything.... 8 zone vales, 5 thermostats, electrics stack vent, out-door-reset/aquastat, etc..
Caution, there can be issues using several 24 volt sources in one residence. That is why have separate RHeating and RCooling terminals for 24 volts to activate unit. If system has only one combo heating and cooling terminals are jumpered
.
@doughness Thank you for your reply and confirmation. Based on the following, I may not even need to worry about 24Vac from the aquastat...
@Astuff, You're correct, the thermostats are not directly connected to the aquastat. Your reply made me look again to see how the current wiring is set up, and while doing that I found something I didn't notice the first time: up high there is already a Honeywell AT72D1683 transformer which is supplying 24Vac to the thermostat on the hot water heater and zone controllers (valves?).
So only the two thermostats (1st floor and basement) are on old, two-wire connections. Given that, my plan is to pull new 18/5 to/from the two thermostats to replace the existing 18/2, and then hook up the Common wire from the AT72D1683 transformer to the Blue wire in the 18/5 bundle to the new thermostat. Does that sound right?
If GoHelloGo has typical system, thermostats contacts start zone valve motor. When valve opens, end switch closes to activate circulator or its controller. Wires from several end switches are connected in parallel to circulator for those zones. DH has 2 circulators activated by 8 send switches.
This another instance of Honeywell causing confusion by labeling L7224 an aquastat when is multi function item..
“The L7224U controls the circulator, oil burner and boiler temperature. “
That transformer is switched thru thermostats to zone valves. The zone valves then activate the boiler.
It would be best to post a picture or two of the wiring at the zone valves to confirm their wiring and C connection.
DH 1057 split level home started with one line feeding all elements. Over years, split to 8 zones, with thermostats and valves in various places and 2 circulators.
When issues arose, diagnostics, trouble shooting and repair was real challenge.
Some years ago brought all thermostat and zone valve wiring, laid out with labels in flow diagram pattern to 2 foot square plywood panel on wall at boiler. Also wires to activate circulator control on boiler and bring 24 VAC. LEDs show what's active.
For this low voltage & current wiring used round casing, interior line AT&T 4 wire #22 wire, and U shaped staples.
DH has long experience with complex systems, likes to simplify things.
When wife question temperature in some room show her boiler temp i.e. 165F then which thermostats and circulators active.
Thanks for the responses. Here are some pictures as @PJmax requested, which should clarify things: first an overall picture of the furnace; second a picture of the 24Vac transformer, and finally the junction box where I will make changes.
Refer to the junction box image: my plan is to replace the Thermostat #1 and #2 wiring which currently is two-wire, with a 18/5 cable, reconnect the two wires as they are today, and then use the Blue wire from the new cable and connect it to the "C" (white) wire from the 24Vac Transformer which is coming in from the top of the Junction box. With that done, my understanding is that I should be able to connect the new wifi thermostat which requires a C wire. Please review and let me know if I am about to do something crazy
First image is furnace, showing three zones (cellar, hot water and 1st floor), and the wiring which goes to the junction box
Furnace
Below is the transformer which supplies 24Vac and enters the junction box at the top AT72D1683 24Vac 40VA Transformer
Junction box showing wires (labeled in image). Thermostat #1 and #2 are two-wire (old), rest are all 18/5, except for T-T and the wires from the transformer. Junction box (yes, it's a mess!)
It's a lot of connections in a small space.
Your transformer may be labeled C and R but it doesn't mean that it was wired that way.
When only two wires is used to connect the stat.... there is no polarity or direction of colors.
What is important is that the one of the transformer leads goes to the R of the thermostat.
The W of the thermostat goes to the TH terminal on the ZV.
The other transformer lead goes to the TR terminal.
On these zone valves.... TH-TR is just a splice point. It doesn't connect to anything in the ZV.
That 4” square electric box is not required for low voltage 24 VAC thermostat wiring. Maze of wire nuts and jumbled wires looks hard to work on.
Terminal 12 strip in link below can join several #18 to # 22 wires and be cut to number needed, Every easy to add or remove wires. Link also has many useful items for heating systems
Here is photo of DH zone control panel mentioned in Post #7 showing easy to see wiring. No zones were active so only LED for 24 volt power was lit.
White page on upper left List 4 step to activate zone and basic color coded wiring for all zones. Labels on right side on have blue tape for thermostats across top and yellow tape wire for zone valves on bottom. Terminal blocks with screw make wiring and changes easy.
Panel is protected by removeable Plexiglass plastic sheet.
A second text sheet, out of picture, at bottom explains color codes and physical location of zone vales.
Bring all zone wiring to central panel makes life easier for both DH and future repair person. Post this hoping it will make it easier for others.
PJmax The wiring is as you show in reply #11 except the C wire not there (yet).
Good news is the rewiring the thermostat #2 in the basement with 18/5 and C wire is complete. Unfortunately ran into a snag (literally) with pulling cable up to the first floor for thermostat #1, and going to stop for the day. More as I get along further.
doughess Your set up is well organized and giving me ideas to do something better than the junction box in the future.
Happy to report that the 1st floor thermostat is also wired up with new 18/5, C wire connected to the smart thermostat, all running perfectly so far. Thanks to PJmaxdoughess and Astuff for taking time to reply to this thread. Much appreciated.
A multizone hydronic system with aquastat can be confusing to wire. Typically if there are multiple zones.... there are zone valves. That means the C will not be coming from the aquastat. It will be coming via the zone valve wiring.
Start a new thread. Reference this one if you want. Post some pictures of your zone valves and wiring.
Hello. I am interested in getting a Nest E diagram of pictures below. I currently have a trane XL 600. Google didnt help with compatibility questions so I thought I'd ask the professionals here. My system has a heat pump and emergency heat and auxiliary heat. The wiring to my current Thermostat is below as well. Is the Nest compatible and also how would i go about wiring it.
Thanks,
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A neighbor asked for help with new thermostat. She said old one was very old and I think electric company may have given her new one. The old one had 2AA batteries in it. She installed it but there is no power at thermostat-nothing lights up. She said when put it on, the furnace came on then went off after a while. I looked at it. She appears to have it wired correctly. It is, if I recall a Rudd furnace, she said 20 years old. at Tstat, the wires are Red, Green, Yellow, White, Blue, with a jumper where Red connects to Rc. I tested voltage between Red and Blue. Got 13V AC. Was expecting 24. Went to furnace and tested the transformer where Tstat wires were connected. Tested between red and blue and got 26V AC. There were 3 red wires, one larger and 2 smaller ones in 2 different brown cables. 3 blue wires, on larger and 2 smaller ones in 2 different brown cables. one red was disconnected but nearly touching and the screw was loose. If it was intentionally disconnected, I wouldn't expect it to be right near screw and screw loose. I reconnected it expecting to find problem solved. Went back up to T stat, but still 13V. I then disconnected the red (that I just reconnected) and the blue at furnace that was in same brown cable. connected red and blue together at T stat and then at furnace checked continuity red and blue, but didn't get any? Of note that brown cable, at furnace, had white wire not used. There was another brown cable that had the yellow unused. perhaps the red or blue at the T stat were from that brown cable? but there was yellow and white at T stat. I should have looked more at some splices up above the furnace to trace better but owner was going to be leaving soon. but stumped by the 13V, and her saying the furnace came on initially? and worked with old thermostat?
01-01-21, 10:39 AM
