But please take a look at the explanation of HI LO and especially DIFF settings found in this companion article: inspectapedia.com/heat/Aquastats.php AQUASTAT CONTROL - home. Check wiring and contacts, relay, temperature setting. The maximum temperature that we recommend you set your radiator output to is 80 °C. Further, the current thermal grease has been improved and doesn't create a stuck-sensor issue any longer. In this article on this other webpage on this site, https://inspectapedia.com/heat/Aquastats.php, it says that, when there's no call for heat, a furnace always will turn on at 10 degrees below the LO set point and turn off when the temp reaches the low point plus the differential MINUS 10 DEREES. The chief cause of a boiler shutting down on reset is typically need of cleaning and maintenance but of course there could be a failing component. This means that there are now 4 zones, 4th being the SuperStor. If you've not interpreted thermographic images before, be advised what you are seeing are low temperatures, less than 80 deg F (26 deg C). a HI-DIFF value is hard-wired in the R8182 series type aquastats, is not adjustable, and no control dial is provided. Continue reading at AQUASTAT LO & DIFF DISABLED or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX. For systems that use coils to heat domestic hot water, the high limit setting is 210°F and the low limit setting 140°F. In the section on keeping the tankless heater hot, don't you mean turn the the Diff control to a higher setting and set the lo control to the lowest settng (120)? Our comments AND illustration of how the DIFF works on aquastats is excerpted direclty from the manufacturer's control installation manual data sheets. For your set-up I don't recommend this, but one can pipe the tankless coil after the outlet from the indirect water heater so that the coil only comes into play as a booster unit if the first heater has run out of hot water. An excerpt from that, given below, forms an argument for setting the DIFF up rather than down. In my case this is ~ 185, after observing a number of cycles. However for a tankless coil case, if no one is drawing hot water, the only thing you need to do would be to set the low limit down to its lowest number. Going to check the temp reading when boiler comes back on,set to 140 low to still give it 20 degree diff from the high even though the high temp is way off maybe due to hard water buildup or something on the sensor on the aquastat .What might be a better Aquastat if I ever change the one I have ? (Feb 28, 2016) Bill said:I have an Oil Fired Boiler forced hot water system (Hydronic) with typical baseboard radiators. So i set my differential to 10 down from 15 since i have a broken coil that i'm not using and trying to save heating fuel and money here in Maine where it's a long winter usually . See above in the article for this justification. Keep you boiler condensing constantly. Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly. Click to Show or Hide Citations & References, AQUASTAT L7224U UNIVERSAL OPERATION & ERROR CODES, AQUASTAT L8124 A-M INSTALLATION & OPERATION MANUAL, AQUASTAT SENSOR PROBE HEAT CONDUCTING COMPOUND, AQUASTAT SENSOR PROBE STUCK in the AQUASTAT WELL, TANKLESS COIL HOT WATER HEATER TEMPERATURE CONTROL, Honeywell L4041A,C Pool Heater Aquastat Controller Instructions, Honeywell L4103A,B,C Combination Aquastat and High Limit, Honeywell L6006 and L6007 Aquastat Controllers, Honeywell R7184 Interrupted Electronic Oil Primary R7184A,B,P,U Installation Instructions. The storage tank has no wires going into the the aquastat of the boiler - the storage tank has it's own aquastat that turns a zone circulator on/off. You're correct that's some heavy equipment can suffer rust damage from condensation when the burner and pilot or left off for long periods of time. The aquastat is a Honeywell L8124C and probably about 15 to 20 years old . So if that is NOT happening either the temperature isn't really 220 (the gauge is inaccurate) OR the TPR valve is unsafe and risks a dangerous, even fatal boiler explosion. It occurred to me that a lot of my confusion over the Low Limit is simply due to their diagram showing an “up arrow” for the Differential Setting. Continue reading at AQUASTAT HI LO DIFF SETTINGS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX. If a conventional boiler is used, each mixing device should be configured to provide inlet temperature protection to prevent sustained flue gas condensation. 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