aquastat settings

JM_5

what should my aquastat be set on? I have a peerless oil fired boiler series WB with a domestic hot water coil that is giving me a little problem. there is a high limit dial with two arms and a circulator dial with two arms. I had the coil cleaned 2 days ago and last night I went from hot shower to warm in minutes.supply valve to the coil is partially opened. should it be open all the way? Thanx

Firedragon_4

Try this:

A common type of controller used in hydronic systems is the triple acting aquastat. Although the control can be purchased by itself, it is normally used as the heart of the hydronic system controller. It allows for the control of the high limit, low limit and circulator functions by a single aquastat control.This basic hydronic system controller is sold by Honeywell as the L8124 and L7124, and by White-Rogers as the 8F43A. It consists of the triple acting aquastat and a built-in switching relay. The triple acting aquastat, a switching relay and a primary control make up the most elaborate of the system controllers for oil-fired systems. They are sold by White-Rodgers as the 6C92 and by Honeywell as the R8182. Let's take a look at how it works. First of all let's look at the easiest part, the high limit, and then the low limit-reverse.

The high limit is adjusted using the knob marked 'HI'. It is marked and adjustable from 130 F to 240 F, and has a fixed differential of 10 F. So, if it is set at 200 F, it will shut the burner off and interrupt power from the B1 terminal 200 F and turn the power on again at 190 F. The terminals marked Black and Yellow relate to this switch.

The low-limit-reverse is adjusted using the knob marked 'LO'. It is marked and adjustable from 110 F to 220 F, and has an adjustable differential of between 10 F and 25 F.

The differential is set using the knob marked 'DIFF'. Now here is where it gets a little complicated in the Honeywell control. If you have the LO set at 180 F with a 10 F differential or DIFF, it will shut the burner off for low limit at 180 F and turn it back on again at 170 F to maintain hot water. The circulator is able to run between these two temperatures. Not too hard to understand so far, but although most of us think that these are the normal settings for any of these controls with this setup they are probably wrong. These settings can lead to short-cycling of the burner and the circulator. With some heating systems like the series-loop, the last room or space on the loop may never get hot enough, because the last piece of radiation may not get hot enough before the pump is shut off by the reverse control.

Another danger is the burner running off the high limit control all winter long. Why? Because the heat never gets out of the boiler fast enough.
Why dangerous?
Because the high limit is a safety control, not an operating control. Now you know why safety and code commercial people demand two high limits. Makes you wonder though, doesn't it?

Now let's take a more difficult example to understand and why everyone just sets the DIFF for 10 F. We will say that the LO is still set at 180 F, but the DIFF is set at 25 F. The burner will come on at 170 F to maintain hot water but, it will shut off at 195 F because of the differential or DIFF setting of 25 F. The circulator can run for heat between 170 F and 195 F, or higher if the burner input can exceed the circulator output in Btu's. This type of operation is common with overfired boilers, under radiated houses, and in zoned systems. The terminals affected by these settings are C1, ZC and ZR in Figure 60. The terminals marked Blue, White and Red relate to this switch.

Now for another example, and to try to get that domestic hot water temperature back to around an average of 175 F. The LO is set at 175 F, with the DIFF set at 20 F. The burner will come on at 165 F to maintain hot water but, it will shut off at 185 F because of the differential or DIFF setting of 20 F. The circulator can run for heat between 165 F and 185 F.

One more, okay? The LO is set at 170 F, with the DIFF set at 15 F. The burner will come on at 160 F to maintain hot water but, it will shut off at 175 F because of the differential or DIFF setting of 15 F. The circulator can run for heat between 160 F and 175 F. Now, are you starting to see the pattern?

Let's lay down a few ground rules about these triple acting aquastats.
1. The reverse always opens at 10 F below the LO setpoint.
2. The low limit always opens at the reverse open, plus the differential.
3. The DIFF setting never has an affect on the HI setting.
4. The LO setting has no affect on the HI setting and vice-versa.
5. The operation of any Honeywell control that incorporates the white block aquastat, operate the same. These include the following controls: L4081, L6081, L8124, L8151, R8182

This copyrighted information is taken from several of our books including our newest text 'HYDRONIC SYSTEMS & WIRING' due out very soon!

George Lanthier, Firedragon Enterprises 2004

Hope it helps!

tom_48

Firedragon,
The aquastat controls the circ. But I noticed it seems to shut the pump down if the low is set to hi, once cold water starts flowing back to boiler, not letting the heat leave the boiler. Should I lower the lo setting? Should I swap out control as the temp. setting dont seem to be correct ( actual boiler temp. )Also, I never seemed to like the idea of maintaining temp. in boiler year round, even though it doesnt use much fuel in the summer for DHW. thanks

Bill Nye_2

The what?

You said if the lo is set to hi?

I'm a bit confused but you need to maintain a minimum of 20° differential between the hi and lo settings. ie 160lo/180hi. Make sure the capillary bulb is fully inserted int the well.

tom_48

Sorry for the confusion. But thats what I meant. The lo setting was set to high on the lo switch, cutting the circ. pump out when the temp in the boiler dropped below the low switch setting. when I raised the low switch setting the circ. pump stayed on letting heated water out of the boiler . Is this right? Im still trying to figure out exactly what George said. I dont think ( according to my interpretation of his post ) that the difference between the lo and hi settings has any "standard settings" ( 160o low/180o high ). But i dont know for sure, thats why im asking. Sorry in advance for more confusion, but Ive asked several "pros" about this switch and nobody really can tell me exactly what it does.

Firedragon_4

That's the most misunderstood

control in our business, FACT!

No other control has as many urban legends around it than that one does! Why? Everybody knows how it works, yeah right!

Okay Tom, try this.

The 'LO' should be set at the point where it just makes hot water less its own differential, 10 F.

The 'DIFF' should be set at between 15 and 20, but never at 10 where it normally is, JMEO! But, important if you want to make adequate hot water.

The 'HI' really doesn't matter that much, mine is set at 220 F. As long as the equipment is correctly fired and sized you shouldn't really worry about it, but 95% of jobs are not right in one form or another. Sorry about that, but it's true.

Best advice is to turn the 'DIFF' to 20 F. Then keep turning the 'LO' down (in 5 f increemnts) until you lose the hot water, then go back up 10 F and you should be all set.

Let us know how you make out.

You can also reference this: http://hbctechlit.honeywell.com/techlit/PDF/95-0000s/95-6571.pdf

Happy heating!

tom_49

Firedragon,
So the high limit is just a safety ( just like limits on FHA furnaces. Im a hot air guy by the way )not actual boiler high temp control. The low setting (w/ diff. ) is really the boiler temp hi/lo control and circ.control. Correct? VERY interesting.
Im gonna go give it another try. I'll keep you posted. I appreciate all the help.
Thanks Tom



Firedragon,
Well heres the update, I turned the high limit up to 200o but the burner kept running till it got to 200o, I just think thats too high for a 40o night. I guess the low limit isnt the hi/lo control afterall, unless my control is NG. Its getting late, I'll try it again tommorrow Thanks tom

oil-2-4-6-gas

.

is this in Long Island? if so a lot of these are set-up without a domestic mixing valve just a manual valve --i would install a mixing valve on the coil --and adjust the control --

eleft_4

Setting

Joel M

Because the hi limit is a safety, that must be why the weil manual says to set it to 215*, up to 250* in severe weather. Apparently the lo limit is the key to what is circulating throug the pipes, right?

Ron Schroeder_2

> The 'LO'

> should be set at the point where it just makes

> hot water less its own differential, 10 F.

>

> The

> 'DIFF' should be set at between 15 and 20, but

> never at 10 where it normally is, JMEO! But,

> important if you want to make adequate hot

> water.

>

> The 'HI' really doesn't matter that

> much, mine is set at 220 F. As long as the

> equipment is correctly fired and sized you

> shouldn't really worry about it, but 95% of jobs

> are not right in one form or another. Sorry

> about that, but it's true.


> Happy heating!




Hi Firedragon,

Are you sure that it is only 95% of the jobs that are not right? I thought it was closer to 99% ;-)

From what I have seen, ALL jobs have less radiation than the boilers output capacity (and oversized boilers too). So when the house calls for heat, 1K1 closes, bypassing the LO Limit, and allowing the boiler to heat up until the HI Limit shuts off the burner. Then if the house is still calling for heat, the burner comes back on as soon as the boiler drops by the preset 10 degree differential. The HI Limit is really not acting like a safety limit in that mode. Only when the house is not calling for heat does the LO Limit control the boiler temp.

So I wouldn't reccomend setting the HI Limit more than the 20 degrees minimum over the low limit unless you have a thermostatic tempering valve on the DHW to prevent scalding. The Hi Limit setting of 220 deg could give mighty hot water out of the tankless while the house is calling for heat.

By the way, when I moved into my house, the LO Limit was set to 160 and the HI limit was set to 240. If I ran the hot water slow enough, I could get steam out of the tap when the house was calling for heat.

Ron

Firedragon_4

Good point on the DHW

side Ron and why I've been promoting 'anti-scald devices' for 10 years.

If you haven't got the new Watts DVD on scalding get it, FACT! It was put together with lots of help from my 'campaign partner' Dave Yates(PAH) and it's a real winner. I'm now showing it in every class I do regardless of the primary subject.

Firedragon_4

You're right Joel,

but it's also for that reason that ASME and others are considering secondary manual reset high limits on everything. Had one on my own house since 1972, because @#%* happens!

Ron Schroeder_2

Hi Firedragon,

Personally I don't think any aquastat that doesn't have a manual reset button is a Safety Limit. What are your thoughts?

Ron

Joel M

How does the manual reset work? Is this something that can be added to an existing install? I assume you mean the honeywell type aquastats can malfunction and water temp goes ballistic? I'm wondering because a few years ago I was talking wiyh the tech servicing my boiler and I mentioned the 250* weil reffered to in the manual and he said "not with these controls" pointing to the honeywell aquastat.

Ron Schroeder_2

Two common ones are the Honeywell L4006E and L4008E. Both are single aquastats that open when the temperature gets up to their setpoint and you must push the red button for them to close. They would be wired in series with the burner control.

Ron

tom_49

Hi Ron,
So your saying that when "tt" closes, the high limit takes over and runs the burner until it comes up to temp. Then when it drops back to below the diff. setting it comes back on. Correct? So when there is no call for heat, the low setting takes over controling the boiler temp. for DHW, which I do have a mixing valve on and watch the HW temp. closely. MAN is that control confusing. Please advise if this is the correct operation. Also, is it correct to say that it is kicking the circ. pump off to allow the temp. to build up in the boiler for DHW use( kinda like priority ).

My boiler is sized right ( or very close )in regards to the amount of BB. But my place on the cape has an old american standard gas boiler 134,000 btu, and only 74' of BB, thats a whole other issue. thanks for all the help Tom

Weezbo

use the low limit to control the boiler .

Ron Schroeder_2

Hi Tom,

Yes, I think you have it right. And the LO Limit keeps the circ from running until the LO limit is satisfied. Not the brightest way of doing things in my opinion especially since the HI Limit differential is unadjustable at 10degrees of less. That can often lead to short cycling.

Ron

Ron Schroeder_2

Hi Weezbo,

That is what I am doing on my own system and several customers. And I set the differential to maximum. But I have an indirect and I use a second relay in series with the B1 contact to fire the burner and I don't use the TT terminals on the 8124.

Ron

Firedragon_4

EVERYTHING CAN FAIL!

Firedragon_4

Right again Ron!

All of the limits we normally use in ALL residential work are considered 'Operating Limits' by ASME and others including the OEM's.

Only a control with a reset button is considered a 'Safety Limit' by insurers and attornies. It's in the official verbage and lexicon of the control business. It's in several books and gets quoted a lot in court.

Firedragon_4

You got it, and

that's why Ron was right about the DHW concern and why it can be a problem when the burner keeps bouncing of the operating limit all winter. There is no safety at that point, FACT!

BTW, unless you have a no-scald device like the Sparco mixer someone can get scalded, FACT! There is a big difference between a mixing or tempering valve and an antiscald valve.

Frank G_2

If you connect the white and red wires, that allows the circulator pump to work immediately when you call for heat rather than waiting until the temp comes up to the lower limit. Any reason why I shouldn't have been doing this?

tom_49

firedragon and ron

Thanks for all the input guys. Im sure there is a better way to control all this stuff, that control just seems outdated. Are you saying I should put in a real high limit inline w/ burner circuit, thats easy.

As far as the anti-scald unit goes I'll be checking on that tommorrow. Thanks again Tom

Firedragon_4

Yeah, you void the UL,

become the manufacturer and in a court of law that makes you fully and completely at fault.

Maine Ken

Is my 8124 defective??? I turned my low limit down to 120 w/ 10 differ and gave a call for heat. My burner ran right up to the high limit setting (180).

I tried different differentials, all went to the high limit.

The only thing my low limit controls as I can see is the low side of my temp settings and my circ. When the temp drops below the low limit = no power for circ.

Thought I had it figured out before, now I am confused.

"Maine" Ken

Ron Schroeder_2

Yup, that's the way they work when wired by the manual.

Ron

Firedragon_4

Yup, and if you're going to

replace it check this out, awesome!
http://hbctechlit.honeywell.com/techlit/PDF/68-0000s/68-0281.pdf

eleft_4

\"Maine\" Ken

That's what the diagram I posted above shows. Call for heat is in the HI limit control area. Check the foot note (1). read it over several times.

Low Limit action...
"SWITCH MAKES R-W AND BREAKS R-B ON TEMPERATURE RISE.WHEN WATER REACHES PROPER TEMPERATURE",

"1) THE BURNER SHUTS OFF OR THE CIRCULATOR PUMP STARTS (IF CALLING FOR HEAT)."

"The call for heat" , in the diagram, is called out in the HI Limit area....... So which, The Low or the High limit turns off the burner when demand is met?..... The text in the diagram says the High Limit controls the call for heat.

Your aquastat is doing just what the diagram shows, so is mine!

al

Firedragon_4

Ooooops, read that wrong

eleft is right, it's okay! SORRY!

eleft_4

Firedragon

George,

As the saying goes," I don't hold a candle" to your knowledge base.

This is what makes this site (The Wall) & (OTT) so important to the comfort industry. A place to discuss and LEARN.

I thank you for your presents and expert professional input on both sites..

And it's free to all!!

al

Firedragon_4

As usual Al,

the professional respect is mutual.

Ron Schroeder_2

> replace it check this out,

> awesome! http://hbctechlit.honeywell.com/techlit/

> PDF/68-0000s/68-0281.pdf




Hi Firedragon,

It really looks nice but they are very vague about the range of differential settings. ;(

Ron

Firedragon_4

I know what you mean Ron,

try reading this one too:
http://hbctechlit.honeywell.com/techlit/PDF/69-0000s/69-1720.pdf

I'm about 1/2 way to finishing a trainer/demostrator for one of these and the Wayne i8124. I'm hoping to play with them next month and learn form the process.

I want to include them in our new Wiring books Volume 1 & 2 in the spring. Right now the big push is to finish our long overdue Hydronics book.

Maine Ken

Thanks for the clarification, I had begun scratching my bald head even balder!!!!