I have a 24 kw ideal logic plus. It’s about 10 years old but this last week or two the water temperature has been intermittent in that sometimes, shower included, the water temperature is fine and sometimes the water is only lukewarm…. Nightmare coz you don’t know if you’re in for a cold shower or a hot one !! Any Ideal experts with some advice as to what may be the problem or why part is playing up ?