This seems like a reasonable explanation. Is it possible to replace the termistor, or is the head replacement the only way?I have heard of this issue with 1900 based printers - it is a feature of the Epson 1900 to prevent the head from overheating. The issue does not usually arise until heavy usage, however. Four to five shirts is not what I would consider heavy usage. The instances I have heard of have been after a few hours of printing and the cure is to turn the machine off for 20 minutes or so and you can then print for a couple more hours before it comes up again. If it is happening after only 4-5 shirts it could be a malfunctioning thermistor on the print head - how old is the print head? Have you tired replacing it?
The printhead is less than a year old and it printed around 1500 shirts.