I was having exactly the same issue with the warm water feeling.. and then in a matter of months started experiencing a burning pain in my lower back, my back would just freeze up when i moved and I couldn't sit or lay down comfortably. I was also experiencing tingling down my arms and in my feet. I went to see my GP who scheduled an xray which showed little and then an MRI which showed a disc bulge. I was referred to a surgeon who scheduled spinal surgery and I had a double discectomy and laminectomy. It turned out my disc was almost 2" into my spinal cord and was pressing on my nerve causing all of my symptoms.
The hot-tap feeing or burning in the legs and /or hip is most likely caused by something pressing on the nerve and the nerve sending referred signals i.e. sciatica.
If you are concerned and if the feeling does not go away by itself or you having tingling and it keeps reoccurring I highly suggest you see your doctor as this can be a symptom of an underlying issue which may in time get worse and you will need to keep an eye on it.
If, like one of the above posts you are losing control of your bladder or bowels this is very serious and you should definitely consult your doctor as soon as possible as this is a sure sign that you spinal cord is suffering in a major way which can lead to long term damage and even paralysis.
I am 35 and my operation was 5 years ago and I am better shape now than I have ever been and get to the gym 4 times a week. Surgery is not the answer for everyone but if you get to the point of surgery, make sure they are a great surgeon!
I suggest you all consult your physicians if you are concerned and as with all things gentle exercise can do great things.. its move it or lose it!