water goes hot and cold?

i had problems for years with my mira 415,and by luck i noticed after turning my water on after a holiday it went ok, then on returning again from holiday, hot and cold showers. the ritual was for my partner to stand at the water tap and once a reasonable flow came through it seemed to do the trick.but this year after replacing my ravenheat boiler. my shower is 1st class.

stan walmsley
June 2010