Aquastat Relay L8148A,E,J High Limit Switch 240 degrees

mike4478

The highest setting is 240 degrees in all these relays. Question is: Is it safe to put it to this setting because this is higher than the water boiling temperature (212 degrees). Is the bulb really sensing the actual water temperature or something else?

STEVEusaPA

In what world would you need or want anything that high? If it shuts off at 240 in a cast iron block the temperature will go up.
If you need a high limit over 180° you have other problems you should address/correct.

You better hope the sensor is accurate as they usually get impaired from properly reading when the well gets a crud build up.

Turn it down...very dangerous.

I'll leave out the part about boiling point of water vs. pressure

mike4478

@STEVEusaPA

The real question is the bulb sensing actual water temp or something else? Why would Aquastat design something and provide an option if it is obviously unsafe or dangerous?

I read in the spec that the bulb senses about 40 degrees higher than the set temperature. So if the high limit is set at 200 degrees, the burner will shut off when the water temp reaches 160 degrees. Would like to know if anyone else can confirm this.

EdTheHeaterMan

The control you are talking about has a component in it that is factory assembled (not field serviceable) that can be used on other controls. That does not mean that you want to use the 240° setting on your equipment. That is why it is adjustable. You know like that is what ice cream comes in flavors other than vanilla. Not every boiler in the world is like you residential heater.

I have the same control on my heater and i have the high limit set at 180°

I have set them as high as 210° in some cases because the home was not getting sufficient heat from
the existing radiators. This higher temperature resolved the "Too cold on the days that the temperature was below 10°F outside", but customer used more fuel at that setting. So I told them they could turn it down to 180° when the cold snap was over. Only put up to 200° when it got colder in the home. And never go above 210° if they needed to. It was kind of a "DIY outdoor reset system for the poor" LOL

But I knew this customer and he could understand the concept. I would not give this option to just anyone. And when the husband dies or someone else moves in, they would need to upgrade the radiation, the insulation, the boiler, or all of the above, to solve the problem.


Respectfully Submitted
Mr. Ed

EBEBRATT-Ed

@mike4478

Most systems are designed to run 180 degree water as the "average" water temp. Most systems are also designed at a 20 degree temperature drop. So if the water leaves the boiler at 190 the baseboard sees and average temperature of 180 and the water returns to the boiler at 170.

This is adequate 90% of the time. So 190 is where I would set the control.

The higher the temperature you run the more fuel you will burn but the house needs less radiation to heat the building

The lower temp you run the more fuel you will save but the house will need more radiation to meet the load.

Nothing wrong with running higher temps as long as this is understood. But why would you want to?


Most systems carry 12 psi minimum water pressure. Water will start to boil at 240 degrees at this pressure. That is why the controls max out at 240

FROM TACO GUID FOR HYDRONIC ENGINEERS, PAGE 2

"PRACTICAL DESIGN TEMPERATURES VARY FROM 170-260. THE DESIGN WATER TEMPERATURE DETERMINES THE SIZE OF THE HEAT DISTRIBUTING UNITS REQUIRED."

"THE USE OF HIGH DESIGN WATER TEMPERATURES IS PRACTICAL AND IS COMMONLY EMPLOYED IN THE UNITED STATES AND CANADA"

This book was probably written in the 50s or 60s long before condensing boilers.

I know of a hospital near me that runs 400 degree high temperature hot water water

STEVEusaPA

mike4478 said:

@STEVEusaPA

The real question is the bulb sensing actual water temp or something else? Why would Aquastat design something and provide an option if it is obviously unsafe or dangerous?

I read in the spec that the bulb senses about 40 degrees higher than the set temperature. So if the high limit is set at 200 degrees, the burner will shut off when the water temp reaches 160 degrees. Would like to know if anyone else can confirm this.

I thought the real question was "...Is it safe to put it to this setting...?" and my opinion is no. I never heard of the 40° about the set level, nor have I ever seen it in practice. It would throw off the lo limit and the differential. But it's an easy check. Run it to high limit, compare the setting to the actual temperature.

One of the safety checks I do on every boiler is disconnect the circulator to see if the boiler shuts off on high limit. So if it's set for 180° and it shuts off on high limit and the gauge reads 180°, that's usually what I see. There is some discrepancy like anything over 5-10 degrees, or it doesn't shut off, I'll change it.

It's pretty hard to convince me any residential system needs over 180° water.

I think @EBEBRATT-Ed answered why the aquastat could go up to hotter temps, with higher pressure. It's not unsafe or dangerous if you use it properly.
Why do cars go faster than 65 if that's the speed limit on most highways?

Or just put in an electronic aquastat.