Hello jody,

How did you conclude the high limit 140°? This is very low temperature limit, are these standard factory presets?

Hello iody,

"what is the differential for boiler aquastates"

I am assuming you mean >aquastats<

Can you tell me if 'Aquastats' is what you want info about please?

See near the bottom for Industrial Boilers.

==========================================

This site explains everything and has switches etc.

http://www.inspect-ny.com/heat/Aquastats.htm

==========================================

This is just a tiny piece from the site above, and seems to answer your questions. But go to the site and get even more details on exactly your model boiler.

--------------------------------------------

• Guide to the functions of a typical heating boiler combination control aquastat like the Honeywell R8182D, the Honeywell L8124A, and the Honeywell L8151A.
• Guide to the Honeywell 6006 Single Function Boiler Limit Control
• How to set the HI LO and DIFF on a heating boiler control
• Heating efficiency and boiler temperature explained
• How to save money by setting the Honeywell R8182D and similar controls optimally Combination Control Differential:
• On this control, the "Diff" or differential control dial specifies the amount below the "Low Limit" to which boiler temperature can fall before the boiler should turn on to keep the boiler warm for making domestic hot water through the tankless coil. Since tankless coils on heating boilers, especially modern small high-efficiency boilers, have rather limited ability to deliver much hot water to the building, most users set the "DIFF" control to its smallest number, assuring that the boiler will come on as soon as possible when it's needed to make hot water out of the heating season.
• What Settings To Use on a Heating Boiler Aquastat Combination Control Lots of people, even some service technicians are confused about the actual function of combination controls and aquastats like the Honeywell R8182D.
• Some don't know how to set the "HI", "LO" and "DIFF" dials on a combination control. Or more commonly, we were taught to just use a "rule of thumb" which set the "HI" to 180 degF and the "LO" to 160 degF. This was certainly a "Safe" setting for this control, and it's in use on millions of heating boilers. But with a little thought, we can adjust these settings and set the heating aquastat control so as to save a bit more on heating cost. ==================================================
• This may also help?
• ==============
• The L4080B is a operating aquastat for a indirect storage tank. I'm pretty sure the differential is fixed at 5 degrees.
  I would use a L4006A. It is a 2 wire aquastat which opens on temp rise. Adjustable limit is 100-240. Adjustable differential is 5-30 degrees. The differential on most high limits is typically 10 degrees fixed. But you can go higher if you prefer on this aquastat.
  Cold start controls like the L8148A with a fixed 10 degree differential are more efficient on fuel usage and will run longer. This is due to the boiler will only start on a call for heat or indirect storage hot water tank call. ========================================
• For Industrial Boilers see below:
• http://www.google.co.uk/search?hl=en&rlz=1T4GGLJ_enGB294GB294&sa=X&oi=spell&resnum=1&ct=result&cd=1&amp;amp;q=differential+for+boiler+aquastats&amp;spell=1 Product Categories for boiler aquastat setting
  Industrial Boilers - (381 companies) Industrial boilers are closed vessels that are used to generate or superheat steam. Activity is produced by the application of heat from combustible fuels, electricity or nuclear energy Heat Output (Capacity):
• Less than 294,000 BTU/hr
• 294,000 to 832,000 BTU/hr
• 832,000 to 2,490,000 BTU/hr
• 2,490,000 to 6,760,000 BTU/hr
• 6,760,000 BTU/hr and up
Maximum Temperature:
• 200 to 200 F
• 240 to 240 F
• 400 to 400 F
• 400 to 400 F
Maximum Pressure:
• 58 to 58 psi
• 100 to 100 psi
• 125 to 125 psi
• 150 to 150 psi
• 160 to 160 psi
Search by Specification | Learn More Boiler Controllers - (54 companies) Boiler controllers monitor and maintain variables such as steam temperature and pressure in order to control a boiler's burner or air mixtureLearn More ============================================

I hope this is the details you are after and they help!

Take care, and good luck...................

Jody,

Typically 'high limit' designates a lock out safety control which requires intervention of some sort...pushing a button,silencing an alarm,depending on your system.

An 'operating' control would control the routine on/off cycles.

Differential is the spread between the on/off temperature setpoints.

Usually you adjust for your max. desired temp. and adjust the 'differential' to attain your desired lower temp. Some are made to work the opposite of what I described.Others have built in,fixed, differential values and you adjust for the max. operating temp. (140 set point,30 diff. = burner/valve off @ 140 and on @ 110).

I can never get my password otherwise I would log in also.

Skies.

Jay.

Greetings.

You asked which kind to get.

The simplest ones that I have worked with (205) have an aquastat single function on the return line to the boiler that is usually set at about 100 degrees F and is in series with the thermostats. And a combination aquastat that has a high limit, thermostat (indoor and outdoor) control, burner control through stack damper control, and circulator pump control and is mounted on the output of the boiler.

The circulating pump is located on the return line back to the boiler. Grundfas and Taco make very dependable pumps some of which have lasted for over 20 years in continuous service.

The system is low pressure usually 15 to 20 psi. In multistory buildings remember that for every foot that you have to go vertically you loose ~ 0.5 psi.

It is usually best to wire the circulating pump to run 24/7 to utilize the heat stored in the system and measured by the single function aquastat on the return line.

If you have an outdoor thermostat in series with the indoor thermostat and return aquastat remember to make sure that it is on the north side of the building and always in the shade to get true outside temperature. This feature is usually used by owners of a building to eliminate boiler usage when the weather outside is over a certain temperature.

The differential is the number of degrees below the low temperature at which the boiler will restart.

Which one to get depends on usage.

If you use the boiler for two zones; for heat and hot water, then you need a dual aqua-stat.

Your high limit is 140 and your differential is 0-5. Differential is regarded as "subtractive-differential". So if you set it 5, cut in will be 135 & cut out 140. At 3 cut in will be 137 & cut out will be 140. If this cut in figure is too low go for a higher differential 0-10. If you want to cut in at 110 you should select a controller with a differential maximum 30. So you cut in at 140-30 = 110 & cut off at 140.You may find a 0-30/ 10-30/ 5-50 depending manufacturer to manufacturer's product.