Yeah, it only goes to 220 degrees but I suppose you can consider anything higher as a problem, you don't need to know the actual temp.
Trouble is where do you point the thing? You'd need about 50 of them I reckon. And will it detect a front 1km away?
The more I think about using thermal cameras the more I think that's the way to go, despite (or maybe because of) me not having any experience with them. Normally we don't recommend any form of image processing with an Arduino but in this case it's nowhere near real time and you are really just looking for a simple pattern with an algorithm like "5 yellow pixels in a row, it's time to go" :)
And there are new Arduinos coming out with plenty of grunt.
I have mate with a system for intruder alarms, he can monitor his shed in QLD from his bus which is currently in WA. I was out there the other day working on something for him and he could see me clearly and direct me in real time to the appropriate shelf when I was looking for some parts. If you used a powerful master board you could have a web server on it and control the entire thing from the web using any browser.
With some cameras (or one that can pan) pointing outwards and a couple more pointing at the house itself you should be able to detect any hot spots. This is an order of magnitude (or two) above what you are thinking about with a few temp sensors, but realistically I can't see a few sensors doing anything useful. Also with cameras you may be able to switch to non-thermal mode and view the property for security reasons like my mate does.
Anyway this may be too much for you as a beginner (I assume) so I won't be offended if you decide to put 3 sensors in and call it a day :) Certainly this should be done a small part at a time, you can always add stuff. So I'd work on getting the Arduino to control the pump, then maybe get it to read and act on an SMS. That will give you a nice remote manual system that's 1000% better than what you currently have. Then with more confidence and more research look into automating the system using cameras or whatever.