Burner Controls on the PB150 Boiler
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Aquastat Relay 11C61
This control is installed on the middle fitting of the domestic coil. These immersion type controls are used with forced hydronic heating systems, which include domestic water service. This model provides high limits, low limits for maintaining minimum boiler water temperature and circulator controls. See the wiring diagram for proper connections of this unit. The primary control is factory wired to the aquastat relay. These controls working as a system will prevent the circulator operation if the water temperature is below a predetermined low level. Likewise, if the water level reaches a predetermined high limit the burner will automatically shut off.
Low Water Cut-off Switch RB-122
This control is installed in the supply tapping in the top front of the boiler. The RB-122 low water control is specifically designed to provide burner cut-off if there is an unsafe water loss, which can result from a broken or leaking radiator or pipe, or a cracked section in the boiler.
SEQUENCE OF OPERATION
Forced Circulation Hot Water System with Tank-less Heater
When the room temperature falls below thermostat setting, thermostat calls for heat switching the control to full burn mode. When water temperature rises to the preset temperature setting on the low limit – circulator control the circulator pump is turned on providing hot water to room zone. At the same time the relay trips and reduces the burner to pilot mode preventing over temperature. If the circulator pump turns off because of low water temperature before the room thermostat is satisfied the relay energizes and switches the burner back to full burn mode to increase the water temperature. This cycling will continue until the room thermostat is satisfied. When the room thermostat is satisfied the burner will switch back into pilot mode waiting for the next heat demand. Because the burner stays in pilot mode between calls for heat, in extended low demand periods the water temperature may rise enough to turn the circulator pump on therefore a dump zone should be configured into the system.
FUNCTIONING OF SAFETY AND OPERATING CONTROLS
The safety and operating controls shall function within the limits specified by the manufacturer for the type of equipment. The following tests shall be performed:
- Check the operation of the automatic fuel feeding interrupt device at each entrance to the floor space within which the fuel-feeding device is installed.
- Check that when the low water level control on steam and hot water boilers is operated to indicate a low water level, the automatic fuel-feed is interrupted.
- Check that when the excessive pressure control on steam and hot water boilers is operated as in an excessive pressure situation, the automatic fuel-feed is interrupted.
- Check that when the excessive water temperature control on hot water boilers is operated to indicate excessive water temperature, the automatic fuel-feed is interrupted and, if appropriate, that one or more zone control valves open.
- Check that if the temperature exceeds 95°C (200°F) in a furnace supply plenum on hot air furnaces, the automatic fuel-feed is interrupted.
- Check that if there is a failure of the fan providing combustion air, the automatic fuel-feed is interrupted.
- Check that if there is a failure of the combustion air supply control mechanism to remain fully open, the automatic fuel-feed is interrupted.
- Check that when the hot water circulating pump manual disconnect switch, is opened, the automatic fuel-feed is interrupted.
- Check that if there is a shutdown or failure of the mechanical flue-gas exhauster, the automatic fuel-feed is interrupted.
- Check that if there is a failure in the flue gas flow, the automatic fuel-feed is interrupted, or the combustion air supply is shut off in manually fuel appliances.
- Check for the proper operation of the minimum fire maintenance controls and system or, if applicable, of the automatic ignition system.
- Check for the proper operation of the controls used for normal automatic fuel feeding.
- Check the operation of any other controls supplied on the appliance by the manufacturer, or required by the authority having jurisdiction.