I have an unvended hot water cylinder; due to low water pressure where I live, I have a pump installed which assists the pressure when using my shower. When I first go to turn my shower on in the morning, it usually takes around 10 seconds from the time that the shower is turned on until any water is produced and the pump is kicked into action; however, if I then turn the shower off and back on, water begins to flow immediately. What would be the reason for this?
As requested: Is this low pressure system for your shower part of a tub also? If the water is being diverted up to a shower head it may take that long to fill the pipe, turn the pressure off the pipe is still full so it flows when turned on. Other than that we would need to know more about the controls on the pump.