Questions and Answers on the High, Low, and DIFF settings of the Aquastat.

A combination of three controls is called an aquastat relay.It is an aquastat, a relay and a transformer.The components are mounted in a gray painted brick with a skinny copper cigar hanging out of the back on a very thin copper tube.The cigar is part of the aquastat.

A place for most of the controls in a boiler system to be wired together is provided by the aquastat relay.There are pairs of screws labeled, for example, T-T, C1-C2, B1-B2 and L1-L2.Terminal screws are used.The label tells you what to do.The two wires from the thermostat would be connected to the T-T terminals.The circulator has C terminals.The B terminal is for the burner.The line voltage is 120V.This means that you don't have to think about the circuits at all.Years before we had that terminology, it was a kind of plug-and-play.

You can't see the circuits inside the aquastat relay.Everything goes into the right place with the help of the aquastat relay.

You wire in line voltage electricity into L1 and L2.A circulator is one of the things that are connected to the aquastat relay.The thermostat is a low voltage item.Line voltage goes directly to the line voltage devices with the circuits inside the aquastat relay.The primary side of the transformer has line voltage going to it.The transformer has a change of 120V into 24V.24V low voltage is provided for the T-T terminals and the gas valve.It will get the correct voltage without you even thinking about it if you wire each device to the right terminals.

If the thermostat calls for heat, the burner and circulator are usually brought on inside the aquastat relay.It's simple enough.You could wire that yourself.The aquastat relay does something special.If the water is already hot enough, the relay keeps the burner off and brings on the circulator.If the water is already hot, we don't need to heat it.The call for heat can be satisfied by circulating the already-hot water.

The aquastat relay has two questions that I get most often.I decided to ask, "Why aren't the parts replaceable?"Chip Troost is the product manager for that control.He knows the whole story because he has been there for a long time.

The L8148 and L8124 are safety controls that go through rigorous testing to assure they are wired correctly and perform to specifications.Allowing parts to be changed in the field without the test equipment to assure proper performance could put the homeowner, service company and the manufacturer at risk.We don't recommend the use of rebuilt controls.They haven't been tested to the rigorous requirements in the documentation.

You can't tell what the differential is when you look at an aquastat relay.

The differential hasn't been specified on the product label before.I don't know why.Boiler manufacturers typically specify a differential that meets their particular appliance design specifications, and perhaps at one time that was seen as proprietary information.

What is differential?You need to specify what control you are talking about.The differential is the difference between when the control opens the switch to stop the heating of the boiler and when it turns back on.

When there is a call for heat and the water temperature is, let's say, room temperature, the control will turn on the energy source.The water in the boiler starts to cool.When the boiler water temperature drops to 160 degrees F (180-degree F set point minus 20- degree F differential), the switch will close and it will heat up again.

The differential is important to reduce fast cycling, which will wear out the components and reduce energy efficiency.Lack-of-heat complaints can occur when the water temperature drops too low.

Depending on the application and what is being controlled, the Make and Break can be adjusted.The differential is subtracted from the Make temperature when cooling controls are adjusted to make at a specified temperature.If it gets too warm, the system turns on and cools until the temperature drops below the Make temperature.Too wide of a differential results in complaints of over-cooling.

I asked if electronic aquastat relays were coming.They are already here for the oil industry.The new L7224 and L7248 series of electronic aquastats provide all sorts of diagnostics that were previously only available on commercial-grade equipment.Communication capability allows for remote monitoring and system diagnostics before the service technician is dispatched to the home.

Chip says that with electronic aquastats you can read the differential setting from the display along with other important settings and operating status.

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The Summit Complex required prefabrication at a lower elevation.