Honeywell L6081A and Taco SR504 - Blowing 6A Fuses

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Old 03-15-14, 10:02 AM
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Honeywell L6081A and Taco SR504 - Blowing 6A Fuses

Hi All -

I recently added both a Taco SR504-4 and a Honeywell L6081A to my boiler to convert the old line volt thermostat and hi limit only (L4081B) setup that came with the house. Its a tankless coil, so Ive used the alternate wiring (warm start) method for the SR504. Unfortunately powering the burner from the ZR of the switching relay (on a call for heat) proves to be too much draw, and I am now popping fuses. Do you have any suggestions for a remedy to this problem? My current though is simply to add an AC to AC solid state relay to the burner control, but I'm not sure thats the right way to handle it.

The current setup is as such:

Hot goes to the lo B terminal on aquastat
ZC goes to W
ZR goes to R
R-R is jumped
Burner hot goes to li H terminal on aquastat
TT is jumped on burner control.

When the low limit is passed on a temp drop, the burner is powered from the hot feed directly. On a call for heat, the burner is powered from the ZR terminal of the SR504. The burner in question is a Beckett SR, which draws 5.8 Amps, dangerously close to the 6A fuse.

Any suggestions before I just add the solid state relay to take the load off the SR504?
 
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Old 03-15-14, 02:01 PM
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OK, so after taking a little time to think this through, I believe I have a workaround without needing the AC to AC relay.

Im simply using the lo side of the aquastat as a 24V thermostat on the 4th zone, and wiring the boiler as if it were a cold start setup.

I had bought the 4 zone switching relay to allow expandability in case I wanted to add an indirect water heater one day. With that 4th zone free, I can use it for hot water production even without the indirect tank. it kicks on the burner, there's just no circulator to run. The 504 even has 4th zone priority to cut the other circulators off while this is active, effectively accomplishing the same thing the aquastat was doing.

I removed the jumper from the TT on the burner, and wired it to the endpoint switch of the SR504. The always on hot leg now goes directly through the hi limit on the aquastat and to the burner. The ZR and ZC terminals in the SR504 are now jumped. I removed the R-R aquastat jumper, and the lo side B-R functions as a low volt thermostat.

I dont exactly know if it meets code, or if its just plain bad form, but do you guys see any reason for concern running the low side as 24V? I have the 18ga thermostat wire wirenutted to the 14ga thhn inside the metal work box. Probably not the best solution, but it seems to work well enough, and takes the burner load off the SR504.

Anyway, would love to hear any opinions on it, for or against.
 
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Old 03-15-14, 03:22 PM
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I'm having trouble visualizing what you've done...

Would it be possible to sketch up a diagram and post it?
 
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Old 03-15-14, 04:02 PM
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Thanks for the reply NJTrooper.

I'm running out to dinner tonight but I can draw up a schematic tomorrow or monday.

Basically, the long and the short of it is; I'm using the lo side R - B breaker as a 24V thermostat. The aquastat now controls zone 4 of the SR, instead of the aquastat firing the burner itself. I know the aquastat is intended for line voltage, but I don't see a problem running low voltage through it, do you?

I had to wire nut the 18ga wire to 14ga wire simply to use the stab terminals on the a'stat. The hi side of the aquastat still cuts power to the burner as usual.

Thanks for looking over this, I appreciate it.
 
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Old 03-16-14, 07:16 AM
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OK, heres the drawing. What do you guys think?

Slightly larger image here:
http://www.badrenovations.com/photos/boiler_wiring.jpg
 
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Old 03-16-14, 10:05 AM
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Guits this looks like a job for the supermen (AKA NJ Trooper, spott, et al .,LOL). I think I can barely follow what you are doing, but as an aside what makes you think that the burner motor is drawing close to the 5.8 max amps specified ? And then even sometimes exceeding 6.0 amps? I guess that sr504 has some 6 amp fuses for individual circuits and one will continually blow when you use ZR as in the warm start configuration.

I probably donít understand motor max amps. My motor on my Beckett AFG draws 2 amps running, and Iíve checked that and itís right on the nose. The specs for mine also say 5.8 amps max. But maybe I donít understand startup and max amps. Maybe mine gets up to 6.0 amps on startup and I just donít know it. But could there be something wrong with your motor? Just throwing stuff out.
 
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Old 03-16-14, 10:16 AM
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Well, simply put, the fact that Im blowing fuses makes me think that Im drawing the max, or more. I cant tell if these fuses are fast or slow blow, the 029 series seems to have both. If fast blow, it could easily happen on startup, even if the motor typically draws under 2 amps. I ordered some slo blow replacement fuses just in case, but I decided the only safe way to fix this was to take the load off the SR504.

Really, all I've done here is wire the boiler up as a cold start application, and use the internal aquastat as a simple thermostat to tell the SR504 to fire the burner. As long as nobody accidentally puts the aquastat R-R jumper back in, or finds some other way to put 120v through the 24v wiring - it should be fine. And now I wont even have to rewire anything if and when we add an indirect water heater.

Anyway, it seems to be working as intended. Back to working on the tankless coil issue.
 
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Old 03-16-14, 02:29 PM
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Guits you got me hooked. My quirky personality. LOL Just trying to learn a little, and with each question I have, then answered, seems to bring up 2 more questions. Oh my. Ignorance is NOT bliss!

But anyway, I found this Q&A stuff below. This was something someone had posted, that supposedly came from the Taco web site Q&A, and this person wanted some clarification about its meaning. Anyway, I could be way off base, but if this was really from the Taco web site, doesnít it seem to say that tying the Taco board ZR to the B terminal of the aquastat to run the burner is OK. I mean isnít that what you did, but it caused problems? I know you arenít imagining blown fuses. Maybe whoever wrote that really didnít know what they were talking about ( a Taco tech fraud LOL)?

But more likely, I am out in lala land and donít understand what they are talking about. lol

Q. I need technical details on how the ZR and ZC terminals interface with the aquastat on a boiler. I wire many boilers and all directions specify cold start or hot start, black box type instructions. I do not fully understand the inner workings, or what happens electrically with either application.
In our Control Instructions, we give two examples: a cold start boiler or a tankless coil boiler. For the cold start, the X, X goes to the TT terminals in the boiler control. For the tankless, the ZC and ZR go to the ZC, ZR terminals of the boiler. Boiler controls that don't have ZC and ZR terminals can be hooked like the cold start.
These hook ups are conditional, in that you move the circulator that was originally wired to C1 and C2 over to the Taco Control.

If you plan to leave the circulator on the boiler aquastat, and a thermostat connected to the TT terminals of the aquastat, you will need to get into the firing circuit of the aquastat. This would be the ZR connection. Run a wire from the ZR of the aquastat to the ZR of the Taco control. If there is no ZR, run a black wire from the ZR of the Taco control to the B terminal of the aquastat.

When an aquastat has the ZC and ZR terminals, the ZC is connected to the low temperature switch of the aquastat and to the ZC terminal of the Taco control.
 
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Old 03-16-14, 02:47 PM
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Yes, theres some good info on Taco's FAQ, which is where i saw that before:

Taco-Hvac

Anyway, yes, it seems that there should not have been any issue with wiring it up the way I had. Perhaps it was a bad batch of fuses. Perhaps they didn't account for an old power hungry dinosaur of a burner. Either way, I didnt want to run the risk of leaving for a ski or snowmobile weekend, and coming home to a frozen waterfall due to broken pipes.

Unless I get word from Taco directly that the SR504 will handle a 10 amp fuse, its just a little too close for comfort. Offloading the burner seems to be a safer move.
 
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Old 03-17-14, 06:18 AM
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Taco customer support got back to me stating that it sounds like the burner is indeed drawing too much. They said I could add a SR501-HC before the 504, which would handle the extra current. I replied asking about the way I have it wired now, so we'll see what they say.

Edit: Taco Support just replied that they dont see any problems with wiring it up this way. That being said, Id still like to hear from anyone else on here with any concerns about it.
 

Last edited by GuitsBoy; 03-17-14 at 07:13 AM.
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Old 03-17-14, 10:05 AM
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I've been waiting for the 'dust to settle' with the questions to Taco support before answering.

I don't see an issue with it myself. In fact, it looks like a clever solution!

I imagine that your burner still has the original motor on it? You could probably reduce the power consumption by going to a newer PSC type motor if there is one that will fit that old burner.
 
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Old 03-17-14, 10:29 AM
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Thanks Trooper.

So do you think I have any NEC or other code violations running 18ga thermostat wire into the aquastat intended for 120V? What about unprotected / exposed low voltage wiring? Right now I have it zip tied to the metallic / armored cable. I don't have anything to go by, since it was all line volt before this.

I was toying with the idea of replacing the burner gun, since its pretty old (Remanufactured 2001), but at this point, I am just trying to hobble along as is until natural gas makes its way down the block. Its 5 houses away right now, but they only provide the first 100 ft, and want $40K to trench the rest. Ouch. One downside to living on a cul-de-sac. Ill have to wait till the neighbors are ready to switch to gas.

We needed to sink a certain amount of money into rewiring the boiler in order to add a third zone, as well as switch to low volt thermostats, but most of this will all be reusable when we switch to a newer NG boiler.

Whats more, with the addition of a pellet stove still year, we cut our oil consumption to a third or less of what it was last year. Somewhere around 300 gallons. All the boiler does is DHW, and possibly the last ten degrees or so of the two secondary zones.

When you add it all up, it doesn't make sense to try and improve the efficiency of the existing boiler. We wont get our money back out of it.

@ zoesdad, take a look at your burner's sticker or plate. Look to see where it says "locked Rotor Amperage". That's the momentary high current draw it takes to get the motor turning from a standstill. You'll see its many times the normal operating current. I think mine is somewhere near 40 amps. It's enough to noticeably dim the lights when it starts. I'm actually impressed the 6 amp fuses lasted as long as they did.
 
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Old 03-17-14, 12:51 PM
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So do you think I have any NEC or other code violations running 18ga thermostat wire into the aquastat intended for 120V?
I wouldn't think it's so much that the aquastat is 'intended' for 120vac but rather the fact that there is low voltage and line voltage in one device. I'm sure there is enough clearance inside, but the fact that it's not LISTED for that use (if in fact it is not) would probably be a shoot down.

What about unprotected / exposed low voltage wiring? Right now I have it zip tied to the metallic / armored cable
That's fine for LV wiring.

One downside to living on a cul-de-sac
I feel your pain. Gas service within 1/4 mile in all directions around our little 'enclave' of homes but since there are only about 10 homes, never gonna see it. Same with city water (which I don't want anyway) and sewers (which I wouldn't mind).
 
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Old 03-17-14, 01:01 PM
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I wouldn't think it's so much that the aquastat is 'intended' for 120vac but rather the fact that there is low voltage and line voltage in one device. I'm sure there is enough clearance inside, but the fact that it's not LISTED for that use (if in fact it is not) would probably be a shoot down.
Yes, that was my main concern in practicality. Induced voltage, or insufficient insulation between the two, but like you said, I'm sure there's ample clearance between banks of contacts.

The concern about NEC violation has more to do with the next guy not knowing whats going on in there. He might not realize Ive got 14 ga intended for low volt only. Hopefully I dont get hit by a bus before gas becomes available.

Oh man, we're within 1/4 mile of sewer service as well, but not a chance we'll ever see it. Ive gotta live out the rest of my days waiting for a stinky sink hole to open up as Im mowing the lawn.
Ol' Andy climbed to freedom through 500 yards of s*** smelling foulness I cant even imagine... Or maybe I just don't want to.
 
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Old 03-17-14, 01:25 PM
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more to do with the next guy not knowing whats going on in there. He might not realize Ive got 14 ga intended for low volt only
Sounds like it's time for a 'hang tag'! Nothing wrong with labeling it!

a stinky sink hole to open up as Im mowing the lawn
And while I didn't drive the mower into it, it IS what prompted the new septic tank installation 2 years ago! Top just caved right in after heavy rains... YECCHCHHHHHHH////
 
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Old 03-17-14, 05:23 PM
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@ zoesdad, take a look at your burner's sticker or plate. Look to see where it says "locked Rotor Amperage". That's the momentary high current draw it takes to get the motor turning from a standstill. You'll see its many times the normal operating current. I think mine is somewhere near 40 amps. It's enough to noticeably dim the lights when it starts. I'm actually impressed the 6 amp fuses lasted as long as they did.
Thanks Guits. I have the real old Beckett AFG and all I can find on the plate is ďThermally ProtectedĒ Voltage= ,Amps=2.0 (and I think HP= something?) But I googled ďlocked rotor ampsĒ and so now I know what you are talking about.

Seems like I have in fact seen ďLRAĒ before (maybe on that very motor on my burner?) But itís hard to read the plate, itís under the control. When I take it out next time Iíll be able to read it better.

Thanks for the education!
 
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Old 03-18-14, 06:53 AM
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Thanks for the education!
My pleasure. And thank you for all your help as well.

NJ Trooper
Hey Trooper, your handle looks familiar. You didn't happen to be a moderator on the old LS1.com forums did you?
 
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Old 03-18-14, 08:54 AM
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You didn't happen to be...
Nope, tweren't me Tony, although I did briefly own a 68 'maro, but that was LONG before they even thought of the LS1!

 
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Old 03-18-14, 08:59 AM
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I did briefly own a 68 'maro
Hands down my favorite year. Loved the body style so much more than the popular 69. My buddy just took possession of a 68 last weekend. Should be a fun project. Sad to hear your ownership can be described as "brief". Thanks again.
 
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Old 03-18-14, 09:04 AM
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Sad to hear your ownership can be described as "brief".
Only because there was a fair amount of profit to be made... didn't wreck! I bought and sold MANY cars back then.

We could talk cars for a while I'm sure, but of course this isn't the place for it...
 
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Old 03-18-14, 10:16 AM
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I emailed Honeywell support a couple times back and fourth to ask their take on using the aquastat in this fashion. They are completely useless. The only thing they could suggest was to have a certified HVAC tech handle the issue, since the intricate equipment is far too sensitive and complex for any homeowner.

With equipment like this, that is so intricate in how your system operates, you definitely want to work with a local HVAC contractor for assistance, to ensure there is no improper handling or damage to the equipment in your home.
And after pressing for more:

If your contractor has any questions or concerns in regard to your case, he/she would be able to call in at 1-800-468-1502, to speak with our contractor support line. However, that line does ask for contracting information, such as company name, before speaking with the caller.
With responses like this, I have to believe that even the most casual follower of these forums is far more qualified to answer the question than their support.

It is working well enough, so I will throw caution to the wind, and blindly leave it as is relying on the hope that the most basic of electronic principles will hold true - at least for the remainder of the time this boiler is in play.
 
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