Single Impellor Pump Problem

[GazPaz]

I have a cold water tank in the loft.
An electric shower.
Between the 2 I need a pump - I have bought a single impellor Triton 450

When the shower was installed - the guy installed the pump off the Mains - stupid I know, but it did work until the pump burnt out after about 7 months! so bought a replacement - but got a different guy in to plumb it in from the tank in the loft.

Problem:

The Pump starts for a couple of seconds and then stops!
The shower works straight of the mains without the pump - but only just - lots of low flow - so not ideal but at least I know the shower works.

The pump works with out the shower - so what is happening?

Help - It is a lot of moeny if I have to replace both!

 

[breezer]

i should guess its the pump pressure switch

electric showers work by putting back pressure on the water so it stays in the shower longer and gets hot. (try taking the shower head off and turn the shower on, it may only just get warm)

but as the pump uses a pressure switch to start and stop, the shower back pressure is causing it to stop