Sounds to me like you may have borderline water pressure. You could check to see that all stopcocks and the like are fully open.
You could also, if possible, take a shower at different parts of the day when less local people are using water.
Finally, turn the temperature dial down a bit. The water will be a bit cooler but the effective pressure will increase - possibly by enough to stop the safety cut-out operating.
Colin
January 2008