Water Boiler Temperature settings and circulator

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Old 12-09-09, 08:08 PM
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Water Boiler Temperature settings and circulator

I have a weil-mclain cg-5 series 12 water boiler in my basement, and am trying to maximize the efficiency.

The way it is currently wired, when there is a demand for heat from thermostat, the boiler kicks on and once the water temp reaches about 145 degrees, the circulator will turn on. When the circulator starts running, the temp slowly drops over about 30 seconds back down to about 120 degrees and then circulator will shut off. The water temp will rise back up to about 145 again, circulator will turn on, temp will drop to 120 and the cycle continues.

The gizmo that adjusts these settings is some kind of Honeywell thing, and there are two settings I can adjust:
#1 - The temp that circulator shuts off at (currently 120), and
#2 - The difference (how much hotter) above the shut off temp before it turns back on (currently set to max of 25 degrees).

I have read that boilers are more efficient at hotter temperatures. Should I adjust any of these settings to improve the efficiency?

Thanks
 
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Old 12-10-09, 07:33 AM
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No, boiler efficiency increases for lower water temp.

Your temperatures are already borderline for causing damaging condensation in the flue. Personally, I would boost them a bit for that reason, but not to improve efficiency.

Is the house staying warm?
 
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Old 12-10-09, 08:04 AM
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The house is okay... it's older and I suspect there is no insulation in some (all?) walls. I have plugged as many drafts as I can find, and that actually made a noticeable difference.

Is there a specific temperature setting you think I should boost it up too?

And on a side note, is there an optimum PSI that the system should be at? After bleeding all the air and adding water, it is in between 10 and 15 psi.

Thanks
 
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Old 12-10-09, 10:04 AM
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Originally Posted by jsherk View Post
And on a side note, is there an optimum PSI that the system should be at? After bleeding all the air and adding water, it is in between 10 and 15 psi.
Depends somewhat on the number of storeys in your house. If it's two storeys and boiler in basement, 12-15 psi, with the boiler cooled down to room temperature, is about right. It will rise as the boiler heats up.

You want sufficient pressure to be able to fill the system and to keep all parts under pressure.

Maybe others here can weigh in on whether and by how much the temp should be raised. It sounds like the boiler temp bounces off a low of 120 deg - at which point, the return temp will be even below that.
 
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Old 12-10-09, 10:10 AM
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Okay, thanks for the help!
 
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Old 12-10-09, 04:51 PM
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Before reading what I wrote below, note that I just re-read your first posting, and realize that you may not be describing what I initially thought you were. So, below the line may be all wrong. But the questions that I asked may still be valid, so answers would probably help.

Are there any model numbers on the Honeywell control?

If you can take pictures, it will help us help you. Free account at Image hosting, free photo sharing & video sharing at Photobucket, upload the pics there, place a link here for us to view the pics.

----------the line----------------------------

What you are describing is a 'triple aquastat', and it's probably an 8124 ? (is there a model number on it?)

The fact that you have a 'triple' leads me to ask:

Do you heat your domestic hot water with the boiler? or do you have a separate water heater?

The HIGH setting on your aquastat is the HIGH LIMIT control, and is the highest temp that the boiler will heat water to during a call for heat.

The LOW setting is the temperature that the boiler will keep itself warm at. This keeping warm is normally used for domestic hot water production.

The DIFF setting works ONLY with the LOW setting, and 20-25 is a good number for that.

Normally, the HIGH is going to be 180F.

The LOW is 'usually' around 140-150 IF and only if you are heating your domestic water with the boiler. If you are not, then you have two choices. Either turn the LOW all the way down, (leave the DIFF at 20-25), OR change the aquastat to a different model that has only the HIGH setting.

What type of heat emitters are in the home? i.e. fin-tube baseboard, in-floor radiant, cast iron radiators, etc.
 
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Old 12-10-09, 05:19 PM
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Yes it is a Honeywell Triple Aquastat Controller Type L6081A.

There are only 2 wires connected to it (that control the circulator). One is connected to the W terminal (diff setting) and the other is connected to the R terminal (low limit temp setting). The schematic says that these two terminals "circuit closes on temp increase". The high limit temp setting knob and terminals are not used.

Note that the aquastat controls when the CIRCULATOR comes on and off, not the boiler. Boiler is controlled by the thermostat on main floor. If thermostat says "I need heat" then boiler comes on. When thermostat says "It's hot enough, no more heat" then the boiler shuts off. Note that the circulator will also shut off (regardless of aquastat settings) when thermostat says "It's hot enough, no more heat".

I have a separate hot water heater tank... boiler is for heat only. I have the old cast iron radiators all thru the house.

So it appears that I probably want to leave the aquastat settings the way they are now (Low Limit Temp = 120 degrees & Diff = 25 degrees).

Thanks
 
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Old 12-10-09, 07:58 PM
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I'm not gonna speculate as to why your boiler is wired the way it is... but we'll talk about the 6081 and other stuff.

Let me try and explain the LOW setpoint.

There is a NEGATIVE 10 differential built in at all times. This means that the bottom of it's control range will always be ten degrees lower than the LOW setting.

Therefore, if your LOW is set at 120, and the DIFF at 25 the 'control range' should be from 110 to 135.

This is because the DIFF ADDS to the LOW setting MINUS TEN.

So, (120 - 10) + 25 = 135

If yours is going from 120 to 145 it probably just means that it's old and out of calibration, and nothing to worry about.

But, the weird thing is, Why does the boiler temp DROP when the circ pump turns on? Isn't the burner still firing at this point?

It sounds to me based on your description that the burner fires as long as the thermostat is calling, is that correct?

I hope that somewhere on your boiler there is another HIGH LIMIT control? If not, what happens if the circulator craps out, and the thermostat calls for heat continuously... will the burner keep burning and burning until it burns down the house?
 
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Old 12-10-09, 08:11 PM
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This is a gas fired system, correct?

Mike brought up an issue that we should talk about...

Firing a boiler that cool is not good for it. The exhaust gases will condense inside the boiler, and flue pipe, and the resulting ACIDIC moisture on the inside of the boiler will eventually rot it out.

But, on the other hand, setting that control higher may not be good for it either! Let's say that you set it for 140 as an example... The boiler would have to get to 165 before the pump turned on, and now you've got cold water from the rads returning to a boiler that is sitting at 165... I mean it was bad enough when it was at 145, but 20 degrees hotter and pouring cold water on it is worse...

How old would you guess the boiler is?

I'm still pondering how come if the burners are still firing the water temp drops so rapidly when the circulator kicks in.

Something not right there... I'm not sure what to suggest.

I think you should post those pictures if you can.
 
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Old 12-10-09, 08:21 PM
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Yes, the burner fires continuously as long as the thermostat is calling for heat.

The temperature that drops is the temperature of the circulating water... water in pipes has cooled down... burner fires and heats up water in boiler... circulator kicks in and starts to move water... hot water leaves and cooler water comes into boiler so the temperature starts to drop back down until circulator shuts off... the water temp then starts to rise again... circulator kicks on again and the pattern repeats. But after a few cycles of the circulator on/off, you notice the water temp is not dropping as much, so warmer water is starting to come back into boiler.

If I cranked the thermostat all the way up and let it run, eventually the water coming back into the boiler would be warm enough that the circulator would run continuously. I was looking at the boiler and I don't see any other types of visible 'high limit' switches on it. Maybe there is an internal one built in? I sure hope so, because you are right... without an internal switch, it would just get hotter and hotter and hotter!

Normally, even in very cold weather, the burner is never on for more than 10 or 15 minutes at any one time... it does not usually take very long to warm up the house!

Thanks
 
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Old 12-10-09, 08:32 PM
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Yes it is gas.

The boiler does not look that old... I would think maybe 5 years, but honestly have no idea how old it is?

I will try to get pics up tomorrow.


Thanks
 
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Old 12-11-09, 05:30 AM
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Two words........Boiler Bypass. Driving too much water through the boiler and it keeps shutting off on low limit. Reduce the flow through the boiler and it won't bounce off the low limit as much.
Bypass_Piping_Explaination
 
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Old 12-11-09, 05:47 AM
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The boiler/burner does NOT shut off at low limit... only the circulator... burner stays on continuously until thermostat tells it to shut off.
 
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Old 12-11-09, 06:04 AM
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The circulator is shutting down on low limit which is called circulator reverse. It is to protect the amount of hot water you can draw from a domestic hot water coil. Your priority is domestic hot water not heat. A boiler bypass not a system bypass will resolve this issue. Less water flow through the boiler, the boiler does not cool down as rapidly.
 
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Old 12-11-09, 06:28 AM
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There is a separate hot water heater... boiler is for house heat only. But I understand what you mean by a boiler bypass and how it would keep warmer water in boiler.
 
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