run tap before shower?

Hi we had a shower put in a while ago but we have to run the hot tap on the basin before any hot comes out of the shower. If you just run the hot on the shower it will run cold for ages and not get warm. Also a pump was put on underneath the bath in a bathroom on the same floor that is now tiled in but the pressure on both showers is rubbish.
Any ideas?Thanks

As an example of an explanation that fits your symptoms, you might have a negative head pump, with a depleted expansion vessel, that isn't reliably detecting flow and therefore not always (or ever) turning on.

However, you haven't yet provided much information about your system, so...

Where is the cold and hot water stored before being fed to the pump - i.e. relative height to the shower head?

And does the pump actually run when it should?

the flow rate from the shower aint enough, to trip the thing, that operates the other thing, that sends a signal to fire up the boiler to give you hot water .

i reckon.

wilhelm said:

the flow rate from the shower aint enough, to trip the thing, that operates the other thing, that sends a signal to fire up the boiler to give you hot water .

i reckon.

Click to expand...

Has shower pump been plumbed in correctly with balanced hot and cold supplies or is cold off mains?

thanks for the replies,
theres two cylinders on the first floor, one with an immersion in it, then there are like 4 tanks in the roof space, 2 are expansion and the other two i assume one is cold water storage and maybe the other one too?

so cylinders are on bottom floor, showers middle floor and tanks on third floor. Now sometimes shower works and sometimes it doesnt.the pump is under the bath in the main batroom and the shower in the ensuite is the problem, there is quite a long run between the two. the cold is off the mains I think, well the pump doesnt run when the showers just on cold and the cold has a good power to it.

maybe running the hot through the basin tap trips the pump into working so thats why i have to do that b4 turning shower on. But then wouldnt the hot at least trickle through the shower when I turn it on without running the basin tap.

I think the pump is in the wrong place too because the pressure in the main bathroom shower is rubbish, the pump is under the bath , shouldnt it be straight off the cylinder? I dont know what type of pump cos its tiled in

thanks for your previous replies