Hayward CHXTBW1930 All Gas Thermostat Bulb Well Replacement for Hayward H-Series Millivolt Pool Heater All gas thermostat bulb well Fits hayward h-series millivolt heater models h1501, h150p1, h2001, h200p1, h2501, h250p1, h100id1, h100idp1 Also fits hayward h-series pool heater models h100id1, h100idp1 Weighs 3 pounds