Lead lag sequencers and alternators automatically control the firing rate, pressure or temperature, in multi-boiler installations for safe and cost-efficient operation. In addition to boiler plant control, applications that benefit from lead lag sequencing include tank-level, air-compressor loading, and air-dryer management. Standard sequencing products range from simple alternators for 2 or 3 boiler plants, to microprocessor-based sequencers with choice of on-off, low-high-off or full-modulation for any number of controlled units. Numerous standard and custom addon functions are available. All sequencers and alternators include building management interface with ASCII-II, and RS-485 Modbus port.