Where to install thermostatic shower pump?

Hello, would you kindly advise where is the best place to install shower pump? I have a gravity system and Wickes bathroom installer advice to fit under the bath but I'm not sure about it if something goes wrong in the future I will have to take off whole bath panel, might deal with tiling etc. So did loft or boiler cupboard would be considered for the installation? Please advise? Regards, Peter