@Ray, I currently have this contactor controlling my pump and would like to avoid having to buy a new device.
http://uk.farnell.com/eaton-moeller/dilm12-10-110v50hz-120v60hz/relay-spst-no-690vac-12a/dp/1110422
datasheet download http://www.farnell.com/datasheets/94707.pdf
The product page says that the coil voltage is 24VAC. I guess this would work, right?