L8148A aquastat questions

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Old 11-17-15, 06:41 AM
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L8148A aquastat questions

I don't know the proper way of starting out here or where to start posing my questions. So in any case maybe someone can tell what is supposed to happen to terminals T-T on any L8148A aquastat. When I look at the circuitry it seems to indicate that if 120vac is supplied to the board via L1 and L2 then if terminals T-T are jumpered together then 24vac is supplied to the coil of the contactor which in turn supplies 120vac to the circulator and burner. Am I right about this? And could someone point me to where I should have posed my question? Thank you.



Separated from... http://www.doityourself.com/forum/bo...-aquastat.html
 

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Old 11-17-15, 10:14 AM
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Welcome to the forums.

At the top of every forum index page you'll see "+post new thread" in a yellow box. You'd click on that and start your thread. I've done that for you here.

You are correct in your theory of operation. What problem(s) are you having ?
 
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Old 11-17-15, 02:58 PM
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T-T are jumpered together then 24vac is supplied to the coil of the contactor which in turn supplies 120vac to the circulator and burner. Am I right about this?
Yes.

There's a little more though.

The relay is TWO POLES. On an 8148, the CIRC will ALWAYS be powered as long as T T is closed.

The BURNER will only be powered if the water is below the setting of the temp dial (minus the diff).
 
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Old 11-18-15, 05:22 AM
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L8148A questions

thank you for getting back to me. I just spent a half hour replying and figuring out how to add an attachment and when I tried to submit it I was asked to log in. I'm logged in now just as I was before. And I lost all of my post. I will try again if this works.
 
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Old 11-18-15, 05:50 AM
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L8148A questions

Furnace Wiring.pdf

This is a restart I hope it works this time. What does auto save mean anyways? Did my previous attempt at posting get saved somewhere?

In any case thank you for the reply.

I now understand that jumpering T to T puts 24vac to the contactor which in turn puts out 120 vac out to the circulator and burner. The burner only if the high limit switch is closed.

The coil on the contactor on the L8148A failed. I put a new one in and it failed too. I bread boarded in a new 120vac to 24vac transformer and fused it and the fuse blows when wired in.

So I'm trying to figure out how all this stuff is supposed work and want to be sure before I fry anything else.

At this point the thermostat circuit before the Aquastat functions properly. 24vdc is provided to all the zone valves and when the thermostat calls for heat the valve de energizes and half of the 24 vdc signal is sent to the distribution strip. If I over ride the contactor it provides 120 vac to the circulator and burner. The circulator runs and the burner fires up. Once the high limit is reached the burner turns off and the circulator continues to run until the thermostat is satisfied.

What confuses me is that the data sheet for the L8148A says it need an input of 24vac at T and T. But when I trace out the circuit it tells me that to get the burner and circulator to run I need to jumper T to T.

So does the 24vdc supplied from the thermostat circuit to the T and T terminals act as jumpering those terminals?

This furnace has been wired as in the diagram and functioning for over 25 years now.

Thank you in advance to anyone who might be able to enlighten me so I can see with my dim bulb of a brain.
Ken Bignoli
 
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Old 11-18-15, 07:41 AM
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Hi Ken,

We need to know a little more...

You mention DC and the diagram shows a bridge rectifier. This is unusual. I suspect that you may have AUTOMAG zone valves?

Can you give us a rundown on the make/model of the boiler, the make/model of the zone valves, the make/model of the thermostats?

the data sheet for the L8148A says it need an input of 24vac at T and T
Not sure what you're reading. I've never seen that in the 8148 docs. They absolutely do NOT require a voltage input at the TT terminals. The ONLY thing that should be applied to the TT terminals is a DRY CONTACT CLOSURE, NO VOLTAGE. Either the internal transformer or the relay coil will be damaged...

So does the 24vdc supplied from the thermostat circuit to the T and T terminals act as jumpering those terminals?
Answered above, no.

This furnace has been wired as in the diagram and functioning for over 25 years now.
I can't speculate at this point how or why it's been working this long.

Might be able to offer some clues after knowing what the various blocks on the diagram are.
 
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Old 11-18-15, 09:33 AM
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Ken Bignoli
There must be some way to answer your questions while I'm looking at them, like you have to me. For later to figure out. I have a hard enough time landing here.

I added the info you requested to my drawing and will attach an update here.

In the mean time. the Specs
Automag AA 24 vdc

Thermostat
White Rogers
SPDT
Type 1F36-335

Aquastat L8148A

Crown Aruba XE boiler
Series 0933 or 0988
Model XE4

Water heater
Carlin Aqua-Mite

When I look at the Honeywell Data sheet 60-2278 for the L8148A it says all models use 24 vac thermostats. When I look at the external connection and internal wiring diagram it shows a 24vac thermostat attached to TT. So this obviously doesn't mean there is 24vac at tt it means the thermostat itself is a 24vac device, I guess. And I know you are correct that by having voltage at TT the transformer and coil of the contactor will be damaged on the aquastat.

I think it can explained why it ran for so long and now it doesn't. Something failed and in my attempt to fix it I probably messed up some of the wiring. This why I'm trying to fully understand how this circuit works. It appears that I need the signals from the 24vdc circuit to act as a dry bridge across T-T and that is what must have been happening before.

I think this is simple application whereas there is a mix of 2 wire and three wire thermostats.

Your insight would be appreciated if you have any further thoughts on this based on the additional info I provided.

Furnace Wiring.pdf

Thank you
 
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Old 11-18-15, 09:50 AM
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Lightbulb

Ken....as you type a reply it get's saved every 15 seconds. If you get disconnected or have a problem accessing the site..... come back to the reply page and look at the bottom of the reply box in the gray area. You should see restore content. Click on that and your typed reply will be restored. This will stay in memory here for quite a while.... days.

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This thread addresses your reply quoting question.... http://www.doityourself.com/forum/ge...ing-reply.html
 

Last edited by PJmax; 11-18-15 at 10:09 AM.
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Old 11-18-15, 10:28 AM
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Hi Ken,

I'll try to find some time tonight to sit and sort this all out for you.
 
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Old 11-18-15, 10:56 AM
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A confusing schematic. I see a connection directly between one valve and a T terminal.

LVR = living room stat.
MBR = master bedroom stat.
2nd FLR = 2nd floor stat.

I see four zones with the domestic water.

What are T1, T2 and T3 ?

The Automag Zone Valves utilize approximately 24 volts DC to close, therefore are identified as a normally-open zone valve. The normally-open feature insures the home owner that hot water will circulate if there is a failure in the power to the zone valve.
 
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Old 11-18-15, 02:51 PM
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What are T1, T2 and T3 ?
I believe they are the thermostats.

therefore are identified as a normally-open zone valve. The normally-open feature insures the home owner that hot water will circulate if there is a failure in the power to the zone valve.
This is also the reason that AutoMag is the recommended 'dump zone' valve for wood boiler systems. When the power goes out, the valve opens and the heat has a zone to dissipate to.

It's going to take me some time to pull the data together... but I will do that later.
 
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Old 11-18-15, 03:41 PM
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T1, T2 and T3 are essentially just terminal strips that are distributions points. These are the common points for all the valve and thermostat wires. I will try to spell these items out more clearly on my diagram.

So T1 is the minus side of the 24vdc and T2 is the plus side. if demand is called for then that signal goes to t3 so as to supply the aquastat with a signal to get the circulator and burner going.

There are four zones, hot water, living room, master bedroom and second floor.

thank you for the tip about the save function, I lost a lot of typing twice.

thanks for the info about quoting too.

This thread addresses your reply quoting question.... http://www.doityourself.com/forum/ge...ing-reply.html
 
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Old 11-18-15, 03:59 PM
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So you are saying that ALL six terminals on T1 are connected together and are 24v +
ALL six terminals on T2 are 24v -
ALL six terminals on T3 are supply to the aquastat.

Do I have that correct ?

You've got + and - assigned to the TT terminals. Wrong. Those TT terminals need to be isolated from the DC supply. If you need to use + and - to activate the TT terminals then you need a relay there.
 
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Old 11-18-15, 07:15 PM
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I'm struggling to login here and keep getting a server error when I try to reply to you.

PJmax, yes all six terminals on each one, T1, T2 and T3 are connected together.

I realize you are correct I need the relay in the circuit to connect T to T and that is where I must have made a wiring error when I first attempted to trouble shoot this. A wire became disconnected from the relay base and I probably compounded my problems by mis wiring it. I think if I can figure out the logic of making a set of relay contacts connecting T to T I will be on my way to a solution. I know from experience having voltage at T - T is a problem. The burning smell from the transformer wiring and contactor coil clued me in. The mission here is to avoid doing that again.
 
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Old 11-19-15, 06:59 AM
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I've figured out what is wrong... but conveying what needs to be done is a different matter...

I'm not sure I am going to be able to make it understandable.
 
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Old 11-19-15, 07:30 AM
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OK, let me try...

I have not fully debugged this in my head yet, but I'm fairly certain this is how you can fix the problem.

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Note that the MBR wiring is REVERSED from the other three valves.

There are two ways to fix this.

1. REVERSE the wiring for the MBR valve and tstat so that it is consistent with the other three.

MOVE the wire from the LEFT HAND T TERMINAL to the T2 terminal strip.

2. REVERSE the wiring for the OTHER THREE valves and tstats so that it is consistent with the MBR valve and LEAVE the left hand T terminal wire where it is on T1
 
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Old 11-19-15, 07:52 AM
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NJT
thank you for taking the time to look at this and providing the diagram. I just installed a new aquastat and it functions properly when T-T is jumpered together. What remains is getting the signal over to it from the thermostat circuit properly.

what you have provided is the missing link. I will need to chew on it for a while before I really see what you're meaning. I want to be able to run the logic through my head so it makes sense to me. It will be easy to verify whether it is correct or not.

Once I get this done and verified I will let you know if I have success or not. Thank you for your help.
Ken Bignoli
 
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Old 11-19-15, 08:16 AM
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The key thing to understand is that you can have ONE SIDE , and ONE SIDE ONLY, of the 24VDC supply connected to ONE of the T T terminals.
 
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Old 11-19-15, 09:08 AM
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thanks for the additonal info. I switched the wires as suggested in first sense you suggested to make all valves and all thermostats similar in wiring convention. That alone did not result in getting an open and closing across the Wires that go to T -T.

I suspect I have mixed up the wiring on the relay base but I have not thoroughly thought thru the logic yet I went directly to try storming.

Interestingly I found that after switching the wires that any combination of water heater and Living room thermostats settings would turn the valves on on off properly. But when I did the same with the master bedroom thermostat and water heater the 2ag fuse blew for the 24v transformer in the dc circuit. I'm going to isolate the master bedroom wiring and see if the remainder of the circuit functions properly.

It will take me a while to think this through, plus I've run out of fuses. I will keep your tip in mind.

thanks
Ken Bignoli
 
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Old 11-19-15, 02:36 PM
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Double check the schematic you drew for accuracy too.

There were some crossing wires that had no 'bump' and no 'dot' so I was unsure if they were connected or not.

If the MBR immediately blew the fuse, perhaps it was not wired backward as your drawing shows?

I think you said that only ONE wire came off... and you were unsure where it went?

How could it have come to there being wiring errors? Did you undo / redo a bunch of wiring?

Make sure that you know which of the thermostat wires are actually the COMMON, NO, and NC terminals. Get that wrong and you could have mysterious trouble.

The way that I see the INTENT of the wiring is this:

When thermostats are NOT calling for heat, the AutoMag valves are ENERGIZED, forcing them CLOSED.

When there is a call for heat, the thermostat changes state from NC to NO and DROPS the voltage to the valves, at the same time connecting the COMMON to the NO which is going to T3 which is going to the OTHER T terminal and completes the contact closure.

Is it possible to post some pics of the wiring just so we can see what you are working with?

At this point, it might just be best to rip it all out and carefully start over.

I will TRY to find time to re-draw your diagram, but don't hold your breath!
 
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Old 11-21-15, 08:49 AM
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One of my missions will be to clean up the wiring diagram and check that it is representative of physical reality. I am not an EE therefore the unclear and incomplete electrical diagrams. Attached are some updates with more sheets with some paths defined in color.

I'm wondering about the MBR circuit too. another task of mine is to insure all the wiring and wires on the thermostats are the same.

Yes there was only one wire off initially but along my lengthy troubleshooting path things may have changed inadvertantly. I kept pretty good track and took a lot of pictures along the way but the fog of war prevailed so I'm not entirely sure of anything. Therefore I need to fix my drawing and insure that it represents the physical circuit. I also did some renovations in the MBR and I could have damaged a wire. I will inspect all that.

I understand the intent as you do. Understanding the wiring to accomplish this is another story.

attached are some pictures and a new set of drawings.

Furnace Wiring 151121.pdf
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Pictured. Top to bottom.
120 to 24 vdc xfrmr
wirebox all valve, furnace and thermostat wires converge
terminal strips T1,T2,T3 left to right
the rectifier is wired directly to terminals on T1 and T2
Relay and base.

thank you for the help
Ken Bignoli
 
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Old 11-22-15, 08:06 AM
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Mornin' Ken,

First thing I see in the pics is that the installers made a boo-boo.

It is not allowed per N.E.C. that 120VAC line and 24VAC low voltage wiring co-exist in the same junction box... at least not without a 'barrier' between them. But that's a whole 'nuther story for a 'nuther time.

Here's where I think the problem is:

One wire is misplaced.

I've removed all the wiring lines and added labels to the destinations for clarity.

The way it's wired now what's happening is that when the thermostats or the WH relay make contact from T2 to T3, the 24VDC is being connected to the T T terminals and in parallel with the secondary of the transformer in the a'stat.

Moving that single wire will correct the issue.

Please review and comment.

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Old 11-22-15, 09:34 AM
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You're going to need to keep the 24vdc from showing up at the TT terminals.

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Old 11-22-15, 06:37 PM
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NJT,

Thanks, great job of explaining all this and most importantly getting me to understand it all. Your marked up circuit made things very understandable.

The swapping of the wire to T-T did the trick. But being gun shy I put a meter on the wires going to T-T and found that I was getting unusual reading on my meter on the MBR circuit, it was switching from continuity to open. I think there is a wiring difference at the thermostat in this circuit. That is why the wiring appeared to be inconsistent with the other thermostats. When I swapped the wires back then all the thermostats indicated continuity properly at T-T upon demand. And no voltage.

Now all works as expected especially after I opened all the service valves in the circuit. All that remains is to set the high temp cutout on the aquastat and button everything back up.

There probably is a good reason not to mix 120 and 24 in the same wire box, I imagine that was defined when we were building our house 30 years ago but not noticed by the inspector.

Again thanks a lot for all the help you gave and effort you put into this.

Ken Bignoli
 
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Old 11-22-15, 06:40 PM
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PJ Max,

Thanks for the help. I just finished modifying the circuit and all works as expected. I really appreciate the help you guys gave me. There is more detailed info in my reply post to NJT

Thanks again,
Ken Bignoli
 
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Old 11-22-15, 07:32 PM
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Glad it all works Ken! Happy heating? (and Thanksgiving soon!)

Pete,

You're going to need to keep the 24vdc from showing up at the TT terminals.
As long as only ONE SIDE of the 24 VDC goes to the ONE of the TT Terminals, no problem. There is not complete circuit... and as you can see, all is well in Bignoliville.

It's like the three terminal Taco valves. You can have two transformers with one leg of each connected together and there's no problem.

If ya need more essplanin, let me know and maybe I can draw up a circuit that show why it's OK.
 
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Old 11-23-15, 04:40 AM
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NJT,

Thanks, all is still working well this morning except the water is too hot. But turning down the thermostat will be easy. It is getting time for the furnace, we have snow on the ground this morning in upstate NY.

Happy thanksgiving to you too. We are looking forward to the day and are thankful for our place and time in the world.

I plan to fix and clean up my diagram for the next time if there is one. If it lasts another 30 years it will get me all the way and then it will be the next persons problem.

thank you for the help and have a good holiday.

Ken Bignoli
 
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