Hayward H250FDN Universal H Series Troubleshooting Guide - Page 7
UHS Sequence of Operation: Normal - gas valve
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UHS Sequence of Operation: Normal The control continually compares the set temp to the actual water temp. When the water temp is 1º below the set point the following sequence starts: 1. The control checks for open blower vacuum switch 2. Blower starts pre-purge cycle as the ignitor heats up (20 Sec). 3. The control checks for a closed blower vacuum switch. 4. At proper ignitor temp, a 4 second trial begins. Gas valve opens and monitors flame sense. The blower will turn off for one second. The ignitor is de-energized at flame sense or at completion of 4 sec trial. If the flame is sensed, The blower vacuum switch, control loop, temp sensor & flame sensor are constantly monitored during call for heat. 5. When set temp is reached, the control ends the call for heat. The gas valve is de-energized, and the flame is extinguished. 6. The blower will operate for a 30 second post purge. NOTE: If during step four, the heater fails to fire, please procced to the next page for more details outlining failure to light operations. 7