This Webasto Air Top 2000 ST STC heater service kit is not voltage specific and will work on both 12v and 24v Webasto heater units. The only voltage specific component found in some Webasto service kits is the glow pin.
If you do require a 24v glow pin for a standard Webasto Air Top 2000 STC 24v please use link - Webasto Air Top 2000 ST C Glowpin 24v 9005087A
Please note - If your heater model is Truck, Renault, Scania or Volvo OE, you may have a Webasto Air Top EVO 2000 STC. In this case you may require the full service kit - Volvo heater Webasto Burner Glow pin Sensor Kit - Air top Evo 2000 | 9034036B | Butler Technik
I hope this helps.