I'm sure this is a classic symptom of a common fault in older boilers but would like to know what the fault is. Central Heating works fine, no probs. Hot water is very unpredictable but usually only works if 1. The heating has been on for at least 60 mins and 2. The tap/shower is only slightly on. As soon as the outlet is opened fully the water temp goes luke warm/cold. Glow Worm compact 100e is the offending piece of ****. Any ideas?