Honeywell L8124A Aquastat question

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Old 07-02-09, 02:06 PM
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Honeywell L8124A Aquastat question

Hello,

I'm new to your forum and am seeking a bit of help.
I would like to bypass the circulator cutout feature on the Aquastat so that my circulator runs whenever there is a call for heat. I installed an Intellidine HW last year and can see how having the circulator run on all heat calls to the boiler would be benificial.
I've looked at the Honeywell manual wiring schematic and it looks like this can be done by running a jumper from L1 to the ZR terminal on the face of the board.
Could someone let me know if this is correct.

Thanks from a new guy
 
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Old 07-04-09, 08:31 AM
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No...

that is not correct.

If you install a jumper from L1 to ZR you will set up a constant call to the burner, and it will continually cycle up to the high limit, shut off, cool a bit, run up to high limit... ad nauseum.

Does your boiler have a domestic coil that provides hot water to the home?
 
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Old 07-10-09, 06:02 AM
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Thank you, I've been on vacation, to better explain...

Regarding the DHW, last winter it was tankless, it has just been reworked and DHW s now supplied via an Amtrol Boilermate WD-7 with a full port zone valve.

The reason for wanting to bypass the Low Limit differential either R-B and or R-W was due to an unwanted effect of the Intellicon HW that i installed last winter. The HW solved my problem of short cycling which is the reason i bought it, but, it created a problem in that there were times when a zone called for heat that the zone valves would open but... the Intellicon prevented the circulator from running, this appears to not be the Intellicon but the Low Limit differential?? The system would simply open the zone valve and be in gravity feed limbo until the temperature dropped enough to trip the low limit differential.
When I installed the Intellicon HW, i understood the effect of the Hi limit but I did not fully understand the Low limit and its differential and am not sure what to do.

I'd like to use the Intellicon regardless of the "savings" as i like the data features and because it eliminates the short cycle problem that i had.

Any suggestions are appreciated. Currently the Hi limit is set at 170, low at 140 and Intellicon is off
 
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Old 07-11-09, 07:49 AM
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Perhaps the easiest solution (and the costliest) would be to replace the aquastat and go to a cold start set up... but if you've read back posts, you know that may have other problems. There's no point in keeping the boiler at 140 if you aren't running the tankless coil, but if the boiler starts to 'weep' when it cools off, then that's the problem. Can't know unless you try it.

Did you say what boiler you have?

You've got zone valves... how is the system wired? i.e. I know that you have the zone valve for the Amtrol, and that means there must be at least one other zone valve for heat zone... describe the full set up... how many heat zones? how connected to the boiler?

The HW doesn't control the circulator at all, only the burner, so it won't be responsible for the circ not running under some circumstances, that's the low limit control on the a'stat doing that.

One thing that you definitely do NOT want to happen is for the Low Limit to call the burner to heat the boiler, and have the circulator kick on and try to pump into a bunch of closed zone valves. Which will happen if you bypass the circulator control in the a'stat.
 
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Old 07-11-09, 04:26 PM
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Which aquasat do you have? The instructions are horrible. The high limit only works when there is a call for heat from the thermostat. The boiler will then cycle between the high setting and ten degrees less as a low limit, or differential.

If the termostat is not active the low dial is a hot water maintenance range from 140-150 if set at 140F.

The basic theory of the Intellidyne is to run at high limit at 180-190 so you get long fire cycles. Who knows why. They build in a long differential to make the long cycle work. So you do not have a short cycle problem. The other question is, what was your short cycle? If it was less than five minutes, your boiler is either overfired or oversized. Running long boiler cycles uses a great deal of oil for no reason. Short cycling would be firing less than 5-7 minutes. It is using too much to get started if too short. The other definition of short cycling is quick start and stop. That is why there is a differential of at least ten degrees.

Indoor reset has all that built in, without any need to change anything. If you go with the Indoor reset you will be in compliance with the DOE requirements for reset control by 2015.
 
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Old 07-13-09, 12:01 PM
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Thank you...... answers to your questions

NJ Trooper........The Burner is a Burnham RS 109 which has 2 heat zones, first and second floor loops.
The two heat zones are wired in accordance with the Taco gold zone valve wiring diagram and the zone for the Amtrol Boilermate uses a seperate transformer just so i didnt tax the heat loop power supply.
Your last note about not wanting the circulator to push into closed zone valves is exactly the reason i sought the advice of this forum.

Exqheat......The Astat is an L8124A, last year prior to the addition of the Amtrol the stat was set at 180 - 150 per the Intellidine folks and all worked fine except for the low limit scenario i described where i would call for heat but the HW was restricting the burner cycle and subsequently restricing the circulator from running. this is where i would like (or would have liked) the circulator to run to use the stored heat in the boiler.
My short cycles were simple, if the first floor called for heat, the boiler would cycle normally, supply the loop and the boiler would run until it reached hi-limit and shut down.. BUT... if 5 minutes later the second floor zone called for heat, then the boiler would refire and repeat the process not using the already heated water in the boiler, the intellidine HW cured this.
I dont have or am not aware of indoor reset?

Given that it sounds like attempting the low limit bypass is something that shouldnt be done would you suggest that i lower the low liming to its lowest of 110F? Right now the AS is set at 170-140
 
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Old 07-13-09, 06:06 PM
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Definitely drop the low side all the way down ind increase the differential to 20-25f.
This will also help change the cycling.
If you guys have not looked at exqheat's product take a look. It is a nice product.
Here is the link.
http://www.exqheat.com/
 
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Old 07-14-09, 09:58 AM
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Thanks again for the replies but I need to question the differential setting, should I be targeting 10 or 25 degree's?? I've looked at the L8124A schematic again and am more confused as ever.

Please help me to understand this if I'm wrong...

From what I read, assuming a 140F degree low limit circulator setting with a 10 degree differential...
On temperature fall, the circulator (R-W) will operate down to the low limit of 140 -10 degrees or 130F actual at which time the circulator R-W cuts out and the burner R-B cuts in to reheat the water. With the 10 degree differential, the temperature rises until the 140F low limit is reached at which time the circulator circuit R-W is made allowing circulation and R-B the burner cuts out "assumidly" allowing the B-R of the hi limit to cut out at its setting..

As i read it, with a 10 degree differential this gives me a 10 degree range where my circulator is disabled by the low limit. If I raise the differential to 25 degrees I simply expand this no circulator range to 25 degrees.

Am I reading and interpreting correctly or am i 180 degrees off..?
 
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Old 07-14-09, 11:39 AM
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The 10 causes the boiler to short cycle and will decrease the efficiency. The 25 will mean longer off cycles and longer run cycles. You have to remember this is going to happen as normal cool down even if nothing is running but the boiler is maintaining temperature. It will not run long to gain the 25 if nothing is running.
 
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Old 07-14-09, 03:42 PM
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I think getting to the bottom of the 'misbehaviour' of your system first requires a good solid understanding of exactly how the Low Limit and the Differential operate... it IS confusicating, and the description in the 8124 doc IS pretty bad...

First, it is important to understand the fact that there is a FIXED 10F NEGATIVE differential built in to the Low Limit. This is why the DIFF control doesn't go below 10... As you say, if you set it to 10, with the LOW at 140, when the boiler COOLS to 130, the burner will fire, and the circ will be disabled. The burner will then continue to fire up to the 140 setting, and shut off, at the same time, the circ will be enabled. The aquastat will NOT disable the circ until the boiler again COOLS to 140 - 10 = 130.

Now let's look at the DIFF control, remembering that with the Low at 140, the BOTTOM of the range will always be 130 (the FIXED -10 Diff). Say you crank the DIFF to 20... leaving the Low at 140. Now, the circ will still only be disabled when the boiler COOLS to 130, but it will not be enabled again until the boiler HEATS to 150. The DIFF ADDS to the BOTTOM of the range.

If you like formulas, try this:

Bottom of control range:

LOW LIMIT - 10 always, regardless of the DIFF setting.

TOP of control range:

(LOW LIMIT - 10) + DIFF

A few examples...

LOW at 150, DIFF at 25

150 - 10 = 140 <-- Bottom of control range

(150 - 10) + 25 = 165 <-- Top of control range.

With these example settings, when the boiler cools to 140, the burner will fire, and the circ will be disabled. The burner will fire up to 165, at which time the circ will be enabled.

Understand that the circ will ONLY be disabled when the boiler COOLS to the LOW - 10 .... all other times it will be free to operate on a heat call, OR a domestic call (which, if you have an indirect, the boiler doesn't know the difference. They both appear to the boiler to be a HEAT DEMAND... same same )

Chew on this a bit and see if it helps ...

NOW, re-read the Intellidyne instructions. If I'm not mistaken, I believe they say NOT to drop the HIGH limit below 180 ! I could be wrong, so check that out. My understanding is that the Intellidyne won't 'economize' at all unless it sees the boiler hit 180 on a heat call. This is my observation of the way the one that I have here works.
 
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Old 11-06-10, 07:10 PM
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OhioFarmBoy, I moved your question to a new thread...

http://forum.doityourself.com/boiler...iofarmboy.html
 
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