![]() “The new L7224 and L7248 series of electronic aquastats provide all sorts of diagnostics that were formerly only available on commercial-grade equipment. He says they're already here for the oil industry. Too wide of a differential results in energy loss and complaints of over-cooling.”įinally, I asked Chip if electronic aquastat relays are coming. Thus, if it gets too warm, the system turns on and cools until the temperature drops below the Make temperature minus the differential. For instance, cooling controls typically are calibrated to Make at a specified temperature, and the differential is subtracted from the Make temperature. “Controls can be calibrated to both the Make (closes switch) temperature and the Break (opens the switch), depending upon the application and what is being controlled. ![]() Too large of a differential can cause lack-of-heat complaints when the water temperature drops too low. “The differential is important to reduce fast cycling, which will wear out the components and reduce energy efficiency. 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 the boiler will begin to heat again. At that time, the switch opens, turning off the energy source. 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 (gas, oil or electric) and continue to allow the boiler to heat until the water reaches 180 degrees F. “For instance, let's say the boiler limit control is set to 180 degrees F and the differential is 20 degrees F. For a high limit-type control where the device is carefully calibrated to switch off (open the switch) at a specified maximum temperature, differential is the 'difference' between when the control opens the switch to stop the heating of the boiler, and the temperature where the switch turns back on because the boiler water has cooled below the set-point minus the differential. What is differential anyway? Chip says, “Well, first you need to specify what control you are talking about. The OEMs (boiler manufacturers) typically specify a differential that meets their particular appliance design specifications, and perhaps at one time that was seen as proprietary information.” They have not been tested to the rigorous requirements in the Honeywell engineering and manufacturing documentation.”Ī second frequent question is, “When I look at an aquastat relay, how can I tell what the differential is?” The answer is, you can't.Ĭhip says, “Historically, the differential has not been specified on the product label. This is the same reason we do not recommend the use of rebuilt controls. Allowing parts to be changed in the field, without the test equipment to assure proper performance after the parts were changed, could put the homeowner, service company and the manufacturer at risk. Chip has been there, well, pretty near forever, and he knows the whole story.Ĭhip says, “The L8148 and L8124 are safety controls that go through rigorous testing to assure they are wired correctly and perform to specifications. I asked Chip Troost, who is the product manager for that control at Honeywell. The first is, “Why aren't the parts replaceable (aquastat, transformer, relay)?” I decided to find out. There are two questions I get most often about the aquastat relay. Circulating the already-hot water can satisfy the call for heat. We don't need to heat the water if it's already hot enough. If there's a call for heat and if, according to the aquastat, the water's already hot enough, the relay keeps the burner off and brings on only the circulator. But here's something special the aquastat relay does. Inside the aquastat relay, if the thermostat calls for heat, normally the burner and the circulator are brought on. It's a kind of plug-and-play, invented years before we had that terminology. What this means is that you don't have to think about the circuits at all. The L terminals are for line voltage (120V). The B terminals are for the burner (oil burner or gas valve). For example, the T-T terminals are where you'd connect the two wires from the thermostat. The label tells you what to wire in there. Take the cover off and you'll see pairs of screws that are labeled, for example, T-T, C1-C2, B1-B2 and L1-L2. The purpose of the aquastat relay is to provide a place for most of the controls in a boiler system to be wired together. The cigar is the temperature-sensing element of the aquastat. ![]() All three components are mounted together in what looks like a gray painted brick, with a skinny copper cigar hanging out of the back on a very thin copper tube. As its name suggests, it's an aquastat, a relay and a transformer. An aquastat relay is a combination of three controls. ![]()
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