Immersiontype controllers that combine high limit protection with low limit and circulator control in forced hydronic heating systems. Provide multizone control by using a separate circulator and R845 Relay for each zone. Include diaphragm powerhead and Micro Switch assembly that respond to temperature changes in boiler water. Mount directly to boiler. Select models include large transformers and extra terminals for supplying power to low voltage zone valves. L8124L1011, Honeywell, Inc., Triple Aquastat Relay, SPST: High & Low Limit