The TAC - Invensys RYB-921-03 is a repair kit for VB-921x-0-4-3.
Honeywell V8043A1029 - Motorized Zone Valve, 3/4" 24V Sweat Conn Low Voltage SKU: V8043A1029 Price: $66.78
Siemens 265-1001 Powers Controls Valve, Electro-Pneumatic 2-Position 3-way SKU: 265-1001 Price: $37.41
Uniline 9204H - Robertshaw Deluxe Mechanical Thermostat SKU: 9204H Price: $13.13
Johnson Controls TEC2101-3 - Electronic Thermostat, Non-Programmable Single Stage SKU: TEC2101-3 Price: $189.23
Honeywell ST9120U1003 - Universal Control Board for Gas Furnaces SKU: ST9120U1003 Price: $80.90