140F to 240F (60C to 116C) Conversion Of Honeywell L8148A Aquastat?

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Old 02-11-16, 09:35 PM
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140F to 240F (60C to 116C) Conversion Of Honeywell L8148A Aquastat?

My existing Honeywell Aquastat has the standard scale range of 180F to 240F (82C to 116C).

I'd like to convert it to the optional range of 140F to 240F (60C to 116C) by replacing the item, called a "high limit controller" (?) circled in the attached photo. Is this possible? How do I go about getting this replacement part

One thing I'm wondering about though is that the high limit controller with the standard range of 180F to 240F has a 15F differential whereas the high limit controller with the optional lower range of 140F to 240F has just a 8F differential. I'd prefer the 15F differential. Wonder why the differentials are different (for different types of applications, I guess). Any insights on this?

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Last edited by OILBTU; 02-11-16 at 10:01 PM.
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Old 02-12-16, 02:51 AM
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Why dont you just replace the whole aqua stat/ relay? I know it will be a bit of money..

On my 180f aqua stat I simply dremmeled the stop on the wheel so I could lower it past 180.


You would have to get a stand alone aquastat and use the well for that to get more of a variety and install a relay next to it for the circ/burner.. Maybe you can utilize that one you have...
 
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Old 02-13-16, 07:57 AM
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Rather than spend money on a old generation Honeywell L8148A aquastat why not spend $20 more for an Out Door Reset unit. ODR's adjusts water temp to changing heat loads, controlling water temperature more efficiently and will save money on oil or gas. The temp dials on older bulb sensing types are not very accurate either for setting temp or as a rough gauge to it. Most new systems come with ODR.

A Tekmar 256 ODR cost only $20 more than the L8148A. It conveniently displays boiler water temp, boiler water target temp and outdoor temp. It has many adjustible settings beyond water temp. Boiler min temp, Max water temp F, adjustable differential 2F to 42F, type of terminals used i.e. baseboard, radiant, and so on. All the things member OILBTU is looking for in one unit.

The 256 ODR needs 24 VAC which you can get from the L818A or someplace else in your system.
 

Last edited by doughess; 02-13-16 at 09:24 AM.
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Old 02-13-16, 01:58 PM
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Yea, I'm trying to do this cheaply but just replacing, potentially, the control unit of the aquastat. But if faced with the purchase of a whole new aquastat, I would probably preferentially look at the boiler "reset" device option.

I now think that I'd like to do some data logging first, in order to decide in what direction to go -- the topic of another thread.
 
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Old 02-13-16, 02:20 PM
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Like I stated simply cut the tab/stop off the wheel on the a stat to lower the temp..
 
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Old 02-13-16, 02:35 PM
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I'll take a look at that. Need to see how this works mechanically. I assume that turning the wheel adjusts spring tension and that that spring tension is applied against some sort of bimetallic arm, in turn regulated by heat transferred from heat sensor, which opens and closes a set of contacts?

Or does the heat from sensor affect aquastat function through some sort of variable resistance electronic device whose output is a function of heat from sensor?

Need to make sure that moving dial beyond limit doesn't mess up functioning of control unit.
 
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Old 02-13-16, 02:47 PM
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Bulb types work by the expansion of gas in it creating a mechanical force/movement of a diaphragm that activates the microswitch. It is not bimetal technology used in many thermal products or involve varying electrical resistance such as used in old automotive gauges.

I would be careful about modifying the mechanism. If it hung up and did not open and shut off the burner, instead of just very hot water the boiler might just blow up with a big boom.
 
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Old 02-13-16, 03:17 PM
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Bulb types work by the expansion of gas in it creating a mechanical force/movement of a diaphragm that activates the microswitch. It is not bimetal technology used in many thermal products or involve varying electrical resistance such as used in old automotive gauges.

I would be careful about modifying the mechanism. If it hung up and did not open and shut off the burner, instead of just very hot water the boiler might just blow up with a big boom.
My opinion but I disagree.. I have repeatable on off from my 180-220 a stat..( that was original config)

I cut the tab many years ago.

I lowered my boiler temp to 140f during shoulder months and up to 160-170f during cold months for 5 plus years now..

Its very very repeatable..


If you can show me documentation to support that the mechanism will get hung up , and why, would be appreciated...
 
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Old 02-13-16, 03:29 PM
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I would be careful about modifying the mechanism. If it hung up and did not open and shut off the burner, instead of just very hot water the boiler might just blow up with a big boom.
Absolutely, this would be my concern knowing that the upper limit is really a safety limit.

In any event, I've decided to put this "project" on hold until I can figure out a way to log data on timing and duration of boiler "on events". Need to be able to measure the outputs before I start messing with the inputs.
 
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Old 02-13-16, 03:46 PM
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This an oil boiler? .
 
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Old 02-13-16, 03:54 PM
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I would look at the beckett if you want to track data... Gas or oil...

https://www.beckettcorp.com/products...oiler-control/
 
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Old 02-13-16, 04:56 PM
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This an oil boiler?
Yes, a Burnham V-84 with a Beckett AWG burner.
 
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Old 02-13-16, 05:30 PM
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Getting Real Heating System Data

I am a firm believer in collecting real data and get the burner actual run time by wiring a clock/elapsed time indicator into the burner solenoid circuit Then accurately measure oil level and correlate with degree days for period. Use the date to calculate degree days per gallon.

Unless you have a good handle on burner efficiency, for a "ball park" number use 80% of 140,000 btu for oil. Then work it out to btu per hour for actual load.

Once you get the basic numbers then it is easy to figure out btu/hour used at design temp of 0 degree F or whatever. The results will be more accurate than one based on building heat load calculations.

Do not want get into a "short cycling" hassle but I would rather have a system run more efficiently twice for 3 minutes at 1X btu, than at decreasing efficiency for 6 minutes or more to get 2X btu. A look at Beckett's stack temperature versus efficiency chart shows why.
 

Last edited by doughess; 02-13-16 at 06:38 PM.
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Old 02-19-16, 10:13 AM
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more on modify L8148A for lower operating T

Mr. Lawrosa,
I like your idea of removing the tab stop to get a lower range on the aquastat. Just to be clear, on the 8148A, the tab is at 210F. After I grind that off, I'll rotate the dial past the old limit marked 180, and then actually be seeing again the marks for 240, 230, 220. So, like, getting 140 would be about at the 220 mark, but off by one complete revolution.
I reckon one downside is that after I'm gone, a pro might look at it and say "it's set for 220, but only going to 140. Must be defective."
 
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