Hello, I am hooking up a switching relay to replace a line voltage thermostat with a 24v one. The manual says to hook up the contact to tt on boiler which I don't have. I will attach a picture of how the boiler is currently wired and the diagram of the taco switching relay. Any help will be appreciated.
Boiler switching relay
- Thread starter Dakota44
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kwired
Electron manager
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- NE Nebraska
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Terminals T and T go to your low voltage thermostat, not to anything on the boiler. That unit then closes the relay which allows burner to run - if aquastat is also saying it is ok to run.
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You left out the diagram of the Taco relay....
kwired
Electron manager
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Maybe I misunderstood something, I though the Zone 1 thermostat and switching relay was replacing a line voltage switch similar to what is shown for zone 2.
If I am wrong, OP needs to tell us what he is adding, and what he is trying to replace it with.
Maybe wants to convert zone 2 to a low voltage thermostat? If so would look fairly similar to how zone 1 was done in that drawing.
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Bingo. And there are no terminals labelled TT connected to the current line voltage unit, so he is confused.
RumRunner
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Another prime example where giving instructions which are haphazardly based on info given by the person asking for help.
As the old adage says: “A good and complete question is half answered,”. . . this iteration is paraphrased by goldigger.
I'm flummoxed myself how you could just say connect the TT line voltage terminal to the 24 v at the proposed replacement relay.
OP distinctly stated that there is no relay contact or any feedback from the boiler which makes it uncontrollable from the 24v replacement.
Shooting from the hip could sometimes shoot yourself in the foot.
And dangerous at best.
I am trying to upload the diagram of the taco switching relay. The drawn diagram is how the boiler is currently wired. I am replacing the line voltage thermostat with a low voltage one for zone 2 via switching relay. There are 2 terminals on the diagram for tt on the boiler at pins 5&6 of the relay. Yes there are also 2 low voltage terminals for tt that go to the thermostat. This is not the question. I will upload the taco diagram
taco sr504-1 wiring - Google Search
https://www.google.com/search?q=tac...C&biw=360&bih=512&dpr=3#imgrc=RANRwduC7PEjsM:
https://www.google.com/search?q=tac...C&biw=360&bih=512&dpr=3#imgrc=RANRwduC7PEjsM:
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- Placerville, CA, USA
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- Retired PV System Designer
Based on that, I see only two concerns:
1. You need to have a constant 120V supply available to power the Taco relay.
2. Ignore the set of output contacts used for TT (actually T and T) and just connect the "circulator" contacts in place of the existing line voltage stat.
The additional set of contacts are used in your Zone 1 setup but are not needed for Zone 2 as currently configured.
I believe that Zone 2 alone cannot currently start the burner.
Sent from my XT1585 using Tapatalk
gar
Senior Member
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180203-1644 EST
Dakota44:
Too many times instructions are given on very specific items like wire numbers, wire colors, terminal numbers or letters, and what connects to what. And these instructions fail to describe the basics of what is being done.
I will start with your first drawing. I have a hard time reading it.
Your original power line thermostat is probably nothing more than a thermally operated SPST switch that closes when room temperature drops below a set-point and does not open until temperature rises above another set-point.
Almost certainly the two set-points are not independent, but are mechanically related, and only one adjustment exists to control both values. The difference between on and off is called hysteresis. There is possibly another independent adjustment that that allows adjustment of the hysteresis.
This thermostat will have only two switch terminals, and thus, two wires to whatever is controlled. Since it is a line voltage thermostat, but it does not require line voltage, it probably can switch higher currents, and tolerate higher voltages than a 24 V thermostat.
It is unlikely the thermostat requires any external or internal power. All power to operate the switch is derived from the thermal power from the variation in room temperature.
You could replace this thermostat with a simple toggle switch, and have a human flip the switch on and off as required. Like putting a log on a fire when more heat was needed.
What is a relay? In the old days in electrical terms it was an electromagnet (isolated from anything else) that magnetically interacted with an armature that in turn could change the state of electrical contacts. Many of these contacts might be isolated from one another, but some might be arranged as a SPDT type of switch.
In general a relay can be considered to be a power amplifier. A small input power can control a large output power.
A 24 volt thermostat is essentially the same thing as a line voltage thermostat except that it is not designed for as high a voltage, and only good for a much lower current.
To use the 24 volt thermostat in a power application we need the thermostat (it is only a switch contact), a relay (has an output switch contact), and a power source for the relay. For very good reasons we need an isolated contact on the relay to control the load.
Your new 24 volt thermostat is basically a SPST switch with two output terminals. Probably closes on low temperature. Thus, only two wires are required from the thermostat to the relay. Likely no power wires to the thermostat, but in an electronic thermostat there may be batteries.
The thing you call a relay is more than a relay, and I don't really know what it is, but I will assume it is simple. By simple I assume it is a 120 to 24 volt transformer, and a 24 volt AC relay coil with a DPDT output contact arrangement.
Looking at the wiring diagram you posted at #9 and the left diagram we see internally what appears to be the output of a DPDT relay.
Terminals N and H at the left are 120 V power to this device. Power must be maintained at all times. N probably means Neutral and H Hot. I don't know that it matters which is which, but use as indicated.
Forget all the other wire connections. All you need is one relay output contact.
Let's consider safety. If you were to loose N to H power you probably would want your relay output contact to open. Suppose you use the left set of contacts with terminals labeled 3, 4, 4 (an absolutely stupid labeling), then I am guessing that 3 and the left 4 are Normally Open with the NO designation meaning that with no power to NH that this contact is open. Do a test on your relay with no power applied and see if 3 to left 4 shows an open circuit. At the same time check that 3 to right 4 shows a short circuit.
The only other question is what the boiler and circulator do or should do when the contacts open from your present line voltage thermostat. If failsafe is in the direction you want, then you want contacts from your relay that open with loss of power to NH.
You do not use any wiring shown in the diagram other than power to N and H, and isolated connections to one output contact.
Wiring from the low voltage thermostat has to be done to get the correct phasing.
.
Dakota44:
Too many times instructions are given on very specific items like wire numbers, wire colors, terminal numbers or letters, and what connects to what. And these instructions fail to describe the basics of what is being done.
I will start with your first drawing. I have a hard time reading it.
Your original power line thermostat is probably nothing more than a thermally operated SPST switch that closes when room temperature drops below a set-point and does not open until temperature rises above another set-point.
Almost certainly the two set-points are not independent, but are mechanically related, and only one adjustment exists to control both values. The difference between on and off is called hysteresis. There is possibly another independent adjustment that that allows adjustment of the hysteresis.
This thermostat will have only two switch terminals, and thus, two wires to whatever is controlled. Since it is a line voltage thermostat, but it does not require line voltage, it probably can switch higher currents, and tolerate higher voltages than a 24 V thermostat.
It is unlikely the thermostat requires any external or internal power. All power to operate the switch is derived from the thermal power from the variation in room temperature.
You could replace this thermostat with a simple toggle switch, and have a human flip the switch on and off as required. Like putting a log on a fire when more heat was needed.
What is a relay? In the old days in electrical terms it was an electromagnet (isolated from anything else) that magnetically interacted with an armature that in turn could change the state of electrical contacts. Many of these contacts might be isolated from one another, but some might be arranged as a SPDT type of switch.
In general a relay can be considered to be a power amplifier. A small input power can control a large output power.
A 24 volt thermostat is essentially the same thing as a line voltage thermostat except that it is not designed for as high a voltage, and only good for a much lower current.
To use the 24 volt thermostat in a power application we need the thermostat (it is only a switch contact), a relay (has an output switch contact), and a power source for the relay. For very good reasons we need an isolated contact on the relay to control the load.
Your new 24 volt thermostat is basically a SPST switch with two output terminals. Probably closes on low temperature. Thus, only two wires are required from the thermostat to the relay. Likely no power wires to the thermostat, but in an electronic thermostat there may be batteries.
The thing you call a relay is more than a relay, and I don't really know what it is, but I will assume it is simple. By simple I assume it is a 120 to 24 volt transformer, and a 24 volt AC relay coil with a DPDT output contact arrangement.
Looking at the wiring diagram you posted at #9 and the left diagram we see internally what appears to be the output of a DPDT relay.
Terminals N and H at the left are 120 V power to this device. Power must be maintained at all times. N probably means Neutral and H Hot. I don't know that it matters which is which, but use as indicated.
Forget all the other wire connections. All you need is one relay output contact.
Let's consider safety. If you were to loose N to H power you probably would want your relay output contact to open. Suppose you use the left set of contacts with terminals labeled 3, 4, 4 (an absolutely stupid labeling), then I am guessing that 3 and the left 4 are Normally Open with the NO designation meaning that with no power to NH that this contact is open. Do a test on your relay with no power applied and see if 3 to left 4 shows an open circuit. At the same time check that 3 to right 4 shows a short circuit.
The only other question is what the boiler and circulator do or should do when the contacts open from your present line voltage thermostat. If failsafe is in the direction you want, then you want contacts from your relay that open with loss of power to NH.
You do not use any wiring shown in the diagram other than power to N and H, and isolated connections to one output contact.
Wiring from the low voltage thermostat has to be done to get the correct phasing.
.
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
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- EC
Kwired is correct. You want to duplicate the relay and wiring for zone 1.
And neither can zone 1. Both thermostats just control their respective circulators, the boiler is a maintained temperature, controlled by the aquastat. However that wiring has me a little confused. That Honeywell part # doesn't come up but I have to believe that it's a simple spst aquastat L6008. (breaks R-B and makes R-W on temperature rise at setpoint). So the way it's wired (or you have it drawn) the zone 2 circulator can only run if the burner is off. What's up with that?
It would be better for you if you just got another RA89A switching relay instead of the Taco and wire it exactly like zone 1 for zone 2. Unless there is some reason for that circulator to only run when the burner is off I would just remove that wire from W on the aquastat.
On the R89A- 2 is neutral, 1&3 are hot and 4 goes to the circulator. If you have to leave the W on the aquastat, DON'T strap 1&3, connect the hot to 1 and the wire from the W aquastat to 3.
As for the Taco, follow the diagram on the left. Wiring is the same as for the R89A. N is neutral, H&3 is hot and 4 goes to the circulator. Again, if you have to use the W from the aquastat, don't strap H and 3. H is hot and 3 is the W from the aquastat.
I shouldn't have to say that the thermostat goes to TT in all cases.
-Hal
And neither can zone 1. Both thermostats just control their respective circulators, the boiler is a maintained temperature, controlled by the aquastat. However that wiring has me a little confused. That Honeywell part # doesn't come up but I have to believe that it's a simple spst aquastat L6008. (breaks R-B and makes R-W on temperature rise at setpoint). So the way it's wired (or you have it drawn) the zone 2 circulator can only run if the burner is off. What's up with that?
It would be better for you if you just got another RA89A switching relay instead of the Taco and wire it exactly like zone 1 for zone 2. Unless there is some reason for that circulator to only run when the burner is off I would just remove that wire from W on the aquastat.
On the R89A- 2 is neutral, 1&3 are hot and 4 goes to the circulator. If you have to leave the W on the aquastat, DON'T strap 1&3, connect the hot to 1 and the wire from the W aquastat to 3.
As for the Taco, follow the diagram on the left. Wiring is the same as for the R89A. N is neutral, H&3 is hot and 4 goes to the circulator. Again, if you have to use the W from the aquastat, don't strap H and 3. H is hot and 3 is the W from the aquastat.
I shouldn't have to say that the thermostat goes to TT in all cases.
-Hal
Thanks for all the replies everyone. I also had a hard time finding info on the honeywell L4081B aqua stat. I found the diagram and will upload it. It appears the reason the circulator for zone 2 is wired through the aquastat is to prevent the circulator from running when the low limit is below the correct setting. this is how the boiler was originally wired and i should have referred this to zone 1. the other zone was added at another date when the house was remodeled and wired differently.
probably the best thing to do would be to rewire everything with a 2 zone switching relay. the boiler will be replaced soon and i will do this at that time. for now i will probably just remove the factory jumper between hot and 3 on the taco and put the N/O contacts (3 & 4) between the circulator and w on the aquastat.
probably the best thing to do would be to rewire everything with a 2 zone switching relay. the boiler will be replaced soon and i will do this at that time. for now i will probably just remove the factory jumper between hot and 3 on the taco and put the N/O contacts (3 & 4) between the circulator and w on the aquastat.
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hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
- Occupation
- EC
Yes! I went to bed last night after I wrote that and woke up thinking hey, now I remember, that's a duel aquastat! Two separate L6008s in one housing, usually labeled high limit and low limit. The low limit B and W close on the temperature rise. It's wired as a low limit for zone 2. Possibly it has fan coils or unit heaters that someone didn't want blowing cold air? Thinking unit heaters too because of the line voltage thermostat.
-Hal
-Hal
kwired
Electron manager
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- NE Nebraska
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- EC
As mentioned aquastat is what controls the boiler itself, your thermostats/relays are controlling circulator pumps. when no call for heat aquastat shuts down boiler on upper limit setting. One you start a zone boiler gives up heat to pumped media and aquastat calls for burner again.
Your T T terminals on your relay are very likely for thermostat that controls the relay.
Your link has way too many pictures - which one is your application.
Your T T terminals on your relay are very likely for thermostat that controls the relay.
Your link has way too many pictures - which one is your application.
peter d
Senior Member
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- New England
I would trash that line voltage thermostat and put in a decent digital low voltage one. Line voltage snap-action t-stats are horribly inaccurate.
All of the pictures I posted is for my current set up. I uploaded a diagram of an aquastat, a diagram of the taco switching relay and a drawn diagram of how the boiler is currently wired. All these are related to how the boiler is wired so I'm not sure how that's too many pics. Yes there is TT for the low voltage thermostat but if you look at the diagram for the taco relay it shows an additional set of TT contacts that go to the boiler. As I mentioned in a previous post I have an idea how I will wire it. Thanks
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
- Occupation
- EC
After two pages I know it can get lost in the discussion, but that is exactly what this thread is about. :happyyes:
-Hal
kwired
Electron manager
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- NE Nebraska
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- EC
Your link in post 9 goes to a google search result for images -and there are more pictures in the results then I care to count. I was trying to ask you to reference a specific one out of those results, which is maybe what you intended to do but didn't work like you wanted it to.
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