it dribbles intermitantly?

Then I can only guess as I have no experience but...

In the documents for my recently installed shower pump much stress was placed on preventing natural air bubbles in the heated water entering the pump else cavitation and excessive wear would result.

Specialist take-off devices can be used...

http://www.imagehoarder.com/pic/83Ft7Eh/9688.jpg

http://77.240.13.10/betterbathrooms/6/5/6577e4fb1c8838bb482e8e7085c55f8b.jpg

the one in the picture is a Surrey Flange but there are others. My plumber was dismissive of these and made the exit pipe from the tank slope at 45º and used a T piece pointing downwards for the hot supply to the pump. Any air bubbles in the water will be directed up the sloping pipe and away from the take-off point.

Like this...

http://www.bathroomexpress.co.uk/images/techflow_turbo_installation_manual_fig4.jpg

Peccavi
July 2009

this is whilst in operation. it dribbles the pump seems to cavitate and then surges when I adjust the temp control.

dan
July 2009

It's a function of age Dan - we all suffer from it eventually.

It won't be the shower pump - unless you can hear it running. My shower head does this too. When the control is turned off water sits up in the shower head. Eventually a drip will allow air in through a hole and a dribble comes out.

One solution may be to remove the shower head and clean out the limescale that partially blocks the holes - then when you turn the mixer control to off the water can drain out properly. It works for me.

Good luck...

Peccavi
July 2009