Generally, the best advice is to get a rolling boil with the lowest amount of heat.
This ^ . Just make sure you get a good hot break and foaming stops until you've got a stable boil going before adding your hops. Even at my first hops addition, I'm sitting right there by the propane tank turning back to heat or ready to kill it completely until I KNOW I'm not going to boil over.
Chances are, if you're questioning at what temperature water boils, you probably don't live in a place of such high elevation. Where are you?
Best thing to do is get yourself a quality thermometer. If you can calibrate yours, great. If not, you can go one of two ways:
1. Get yourself an oven thermometer (don't submerge the probe too close to the wire!) this way, you can put a set temperature alarm to go off when you hit the temp you want. Set your steeping grains for 155 degrees and walk away (not too far though!). Come back, turn the alarm off, toss the grains in. Use the timer function to set it for 20 or 30 minutes this time. Come back and then set it for 200 degrees (water for me boils at 212). This gives you enough time to hear it going off if you miss it as well as tame any boilovers waiting to happen.
Check out this model sold by Amazon. A good quality thermometer in that style is hard to come by (most complaints tend to come from the probe, so be prepared to replace it) but this is one of the more popular, better rated ones.
http://www.amazon.com/dp/B0019R4HQQ/?tag=skimlinks_replacement-20
2. Just get a quality instant read probe style thermometer and don't stray too far from the pot. The ones in the links below are great because they have the fastest read time for the price at 5 - 6 seconds (they are made by ThermoWorks who make the ThermaPen which has a 3 second readout but costs $90; worth it to some but not me right now), but more importantly for cooking (and sanitation purposes come to think of it) it has a very small probe which is great in the kitchen as you can take accurate temps of very small cuts of meat and without boring a huge hole in it and loosing the natural juices. They're a great investment and
very reasonably priced. I own the first one listed but understand it lacks the calibration screw (I don't think I'll need it quite honestly) but the second one has a larger readout (get this is you have crap vision) however, is topheavy and awkward if you were to clip it to an apron or otherwise. I've used both and they're practically the same exact thing, just choose a style based on personal use and preference.
http://www.amazon.com/dp/B002GE2XF8/?tag=skimlinks_replacement-20
http://www.amazon.com/dp/B002GE9S8I/?tag=skimlinks_replacement-20
Edit: I just learned they also make a waterproof version (the other two above are water-resistant which can probably be dunked without adverse effect but you can't depend on more than that). They've also increased the maximum range which is great if you ever do any sort of frying. On top of all of THAT, it's the same price as the other two! The only downside is the tip is a big larger which is a non-issue if you're using it to brew. Order it, or any of the other listed thermometers from the company directly.
http://www.thermoworks.com/products/low_cost/rt600b.html
http://www.thermoworks.com/