Water should be boiling, not just hot. When you say 'heat up water', it suggests it's not at the point of vigorous boil to really extract the flavour. Allow me to quote Douglas Adams:
"One or two Americans have asked me why it is that the English like tea so much, which never seems to them to be a very good drink. To understand, you have to know how to make it properly.
There is a very simple principle to the making of tea and it's this - to get the proper flavour of tea, the water has to be boiling (not boiled) when it hits the tea leaves. If it's merely hot then the tea will be insipid. That's why we English have these odd rituals, such as warming the teapot first (so as not to cause the boiling water to cool down too fast as it hits the pot). And that's why the American habit of bringing a teacup, a tea bag and a pot of hot water to the table is merely the perfect way of making a thin, pale, watery cup of tea that nobody in their right mind would want to drink. The Americans are all mystified about why the English make such a big thing out of tea because most Americans have never had a good cup of tea. That's why they don't understand. In fact the truth of the matter is that most English people don't know how to make tea any more either, and most people drink cheap instant coffee instead, which is a pity, and gives Americans the impression that the English are just generally clueless about hot stimulants. "
"One or two Americans have asked me why it is that the English like tea so much, which never seems to them to be a very good drink. To understand, you have to know how to make it properly.
There is a very simple principle to the making of tea and it's this - to get the proper flavour of tea, the water has to be boiling (not boiled) when it hits the tea leaves. If it's merely hot then the tea will be insipid. That's why we English have these odd rituals, such as warming the teapot first (so as not to cause the boiling water to cool down too fast as it hits the pot). And that's why the American habit of bringing a teacup, a tea bag and a pot of hot water to the table is merely the perfect way of making a thin, pale, watery cup of tea that nobody in their right mind would want to drink. The Americans are all mystified about why the English make such a big thing out of tea because most Americans have never had a good cup of tea. That's why they don't understand. In fact the truth of the matter is that most English people don't know how to make tea any more either, and most people drink cheap instant coffee instead, which is a pity, and gives Americans the impression that the English are just generally clueless about hot stimulants. "
http://www.bbc.co.uk/dna/h2g2/A61345