I have added a shower pump to the hot supply to a mixer shower. The mixer shower is a Mira and is about a year old. It had worked fine but wasn't very powerful. The shower is in a bungalow and supplied by a gravity fed system. On initial testing the new pump installation was a success. But now it is temperamental. The shower output pulsates and correspondingly the pump is kicking in and out (on for a second off for a second). I can stop the pulsating in one of 2 different ways: 1. by removing the shower head. And 2 by turning the temperature up to it's hottest setting and then slowly reducing the temperature back to the required temperature. But the next time the shower is used the problem returns. Any ideas or advice as to how I can overcome the problem would be greatly appreciated.