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The temperature must be set below the lowest permissible temperature for any system related component affected by boiler supply water. Under no circumstances can the high limit aquastat be set higher than 250°F. I. BOILER MODULATING CONTROL - Various controls are used to modulate burner firing rates. No attempt will be made to cover every possibility, however a general outline will be given. Most modulation controls require the entry of a boiler temperature identifying boiler operation at the maximum firing rate. A boiler operating temperature below that will also generate a full firing rate. When a boiler heat demand is generated the unit will initiate at either a low or high fire rate and quickly ramp up to the high fire rate. The unit will continue to fire at the high fire rate until the boiler high fire modulating limit is reached. Many modulation controls require the entry of a burner off or low fire setting. The burner will modulate between the high fire and low fire rate based on the absolute boiler temperature as well as the rate of change in boiler temperature. If using a T991 Proportional Control or a similar modulating device in a traditional hydronic system, the minimum setting shall be the sum of the designed heating system return temperature + boiler AT + 10°F. Example: System Supply 180°F System Return 160°F System AT 20°F Boiler AT 40°F Min. Setting = 160°F + 40°F + 10°F =210°F *NOTE: A higher flow through the boiler, achieving a 20°F AT would lower the minimum to 190°F. If using the same control in a system where the designed return is less than 135°F, then the minimum becomes: 135°F + Boiler AT + 10°F J. TEST CONTROLS WARNING Before installation of the boiler is considered complete, the operation of the boiler controls should be checked, particularly the low water cutoff and the high limit control. All controls must be checked prior to putting the boiler in service. 1. CHECK OPERATING CONTROL OPERATION. Raise and lower operating control setting as required to start and stop burner. 2. CHECK OPERATION OF HIGH LIMIT CONTROL — Jumper Operating Control Terminals. Allow burner to operate until shutdown by limit. Installation is not considered complete until this check has been made. REMOVE JUMPER. 3. CHECK LOW WATER CUTOFF control with water level at normal water line (see Figure 1). Raise operating control setting to allow burner to operate. Open boiler drain to allow water level to drop to bottom of sight glass until burner operation is shut down by low water cutoff. Close boiler drain and refill to normal water line. Burner should automatically restart during fill. RESET OPERATING CONTROL. 50 CAUTION Probe and float type low water cutoff devices require annual inspection and maintenance. 4. CHECK OPERATING CONTROL on boiler equipped with tankless heaters. With burner off, draw hot water until burner starts, then turn off hot water and check burner shutdown. 5. CHECK RTC CONTROL - see the Test Section in the RTC Installation and Maintenance Manual. K. BOILER AND SYSTEM CLEANING - STEAM BOILER NOTICE A qualified water treatment chemical specialist should be consulted for recommendations regarding appropriate chemical compounds and concentrations which are compatible with local environmental regulations. WARNING Chemicals used in treating boiler water are toxic and/or harmful. Always use protective clothing and equipment when working with/near chemicals. Contact local authorities to determine if treated boiler water can be discharged into local waste water system. 1. Oil, greases & sediments which accumulate in a new boiler and piping must be removed in order to prevent an unsteady water line and carry over of the water into the supply main above boiler. Operate the boiler with steam in the entire system for a few days allowing the condensate to return to the boiler. If the condensate can temporarily be wasted, operate boiler only for the length of time it takes for condensate to run clear. If the latter cannot be achieved or if the condensate is returned to the boiler, boil out the boiler using the SURFACE BLOWOFF connection. See Figure 40a. a. Drain boiler until water is just visible in gauge glass. Run temporarily 1/” pipe line from the surface blowoff connection to an open drain or some other location where hot water may be discharged safely. Do not install valve in this line. b. Add an appropriate amount of recommended boilout compounds. c. Start burner and operate sufficiently to boil the water without producing steam pressure. Boil for about 5 hours. Open boiler feed pipe sufficiently to permit a steady trickle of water from the surface blowoff pipe. Continue this slow boiling and trickle of overflow for several hours until the water coming from the overflow is clear. d. Stop burner and drain boiler in a manner and to a location that hot water can be discharged with safety. e. Refill boiler to normal water line. If water in gauge glass does not appea...

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