I have a Grundfoss 1.5 STC shower pump which has been working fine for the last couple of years. We have recently had some plumbing work done which required disconnection of the pump, and since then, after a couple of OK showers, it no longer works properly. The hot water feed seems to be the source of the trouble as it can slow down or stop altogether with the note of the pump changing to a rough uneven sound. With the pump switched off and only gravity feed driving the shower there is a sort of crackling noise on the hot water side which I took to be a sign of air in the system and the source of my problem. However, after extensive investigation I am now beginning to doubt this and wonder if the pump itself has developed a fault independent of the plumbing works mentioned. Does anyone know if this crackling sound is symptomatic of a pump problem and what it might be? The plumbing to the pump is by Surrey flange on the HW side and separate feed from the cold tank on the CW side. By the way, I'm trying to get the plumber back to advise me on this but he is proving elusive!