Bristan Artisan shower mixer will not start pump

[dquinn]

We had a Bristan Artisan recessed shower fitted over a year ago and since installation it will not start the pump when switched on. We have to turn a hot tap on at the basin to get the pump to kick into life.

The pump feeds a bath mixer tap, a basin mixer tap and the shower. Both the bath and basin start the pump straight away but the shower will run forever even on the hottest setting without starting the pump. As soon as we activate a tap, the pump kicks in and the shower starts getting hot water. If the shower is turned off, it will not start the pump again even if turned back on immediately.

The installers swapped the pump for a negative-head model but have since gone out of business and we've been using the basin tap to kick the shower into life but It's niggling me that it should work and doesn't!

I had thought about changing the thermostatic valve in the shower but I'm not sure that will fix it. Any ideas?

 

[adam84]

Most modern shower pumps are either "positive" head or "negative" head, this means that there are certain installation requirements for each pump. Negative head pumps require a shorter "head" above the pump meaning there has to be a certain amount of pressure/flow to activate the pump, by opening another tap/outlet to fire the shower pump it sounds like pump has been incorrectly installed or under sized.