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I would recommend contacting the original roofer again and inform him that the roof is still leaking. Give him the opportunity to come out and repair the leak again. He may need to hire a leak detection company in order to locate the source of the leak. Water can travel along beams and trusses and end up in a location that is a good distance from the source itself.

There are usually time limitations on warranties, but if the roof initially leaked within the warranty time then the roofer should be responsible for making the roof free from leaks. Because so much time has passed you may want to hire a professional to come in and inspect for mold. Building materials wet for extended for amounts of time will undoubtedly have mold growing on them.

You should also bring this to the attention of your homeowners insurance company. Roof leaks are typically covered under the terms of your policy and could pay for the majority of the repair costs.

If the original roofer cannot fix this then you need to hire another roofer with the ability to fix the leak. The most important point is to keep water out of your home to prevent further damage.

If the roofer is non-responsive and not willing to take responsibility for the roof then you may want to consult with an attorney to review the terms of your intial contract.

Feel free to post any follow-up questions you may have.

Jay is right. The roofer should know how to properly go about leak detection. A leak detection company is a experienced roofer who knows what he is doing. You actually know more about leak detection than your roofer! Where did the rain fall that you did not spray with the hose?
Here is a continuing Ed course designed for contractors who are involved with roof leaks. It should give you more ideas to locate your leak source.
Roof Leak Detection - Red Vector continuing Ed.
Since shingles are the most common roofing material for residences in this country, let us start with them. When you first arrive at the house with the leak, do you go right away onto the roof to inspect it? It does not hurt to give it a visual inspection, although the real detection often begins when you go into the attic. The reason for this is simply that a visual inspection frequently does not reveal the source of the leak. Of course, we know to check the chimney, if any; the vent pipes and stack pipes; the skylight(s), if any; and all other intrusions. We know to observe for: raised nails,curled, cracked, or broken shingles missing tabs or shingles and lifted shingles But this inspection often just does not show us the cause of the problem. An inspection in the attic much more easily pinpoints the place where the water is entering. Even if the roof sheathing is not still wet, the plywood (or waferboard, or whatever constitutes the roof sheathing), will show discoloration where the water has entered and run, even though it may be dry now. This might not seem so important, but the ability to distinguish between water discolored wood and a naturally occurring discoloration without having to crawl across trusses or joists through the insulation is a big plus to you. Particularly when the crawl space in the attic is shallow and there isn't much room to manuever, it is a real Godsend! piece of equipment that is essential is a good pair of binoculars. Many of the places that are, as a practical matter, inaccessible to you due to the shallowness of the roof (such as at the edge of the building), can be seen with the aid of a powerful light and a good pair of binoculars. It is not always easy to see a drop of water at 30, 40, or 50 feet with the naked eye. But it becomes doable with light and lens. Your job in the attic is to find that drop of water (or where it has been). These tools will greatly help you. When you do find the wet or discolored place where the water is entering, mark the highest point of it. The most common way of doing this is to drive a nail or screw a screw up through the roof at the exact point of water entry. This does no harm, because you will be repairing that exact area anyway. But when you go out and get on the roof, you will be able to absolutely pinpoint the spot that is causing the trouble. The leak will be at the marked point or higher. Another way to exactly locate the spot where the water first enters is to precisely measure from the place that you have visually located in the attic to three other fixed and identifiable places on the roof. For example, you might triangulate between the northeast corner of the chimney, the southeast corner of the water heater vent pipe, and the west side of the master bathroom vent pipe. It is usually best to write these measurements down as you take them. And remember to be precise. Looks can be deceiving. The exterior of the roof sometimes looks a little different to you in distances than the interior does. If the cause of the leak is hidden, a very precise measurement can save you having to remove shingles unnecessarily. And now we come to the artful part of leak detection on shingle roofs. What happens if you go in the attic, you find water dripping out of one isolated spot, you mark it and go up onto the roof, and there is nothing there to indicate any possibility of a leak?!! It happens! What then? Without sounding too simplistic (and not trying to be funny), we start with the very basic knowledge that water flows downhill most of the time. Certainly, capillary action will make water move upward in materials with the right porosity and surface finish. And of course running water will push water uphill for short distances. But these factors can be eliminated by observing the particular situation and determining if the right facts are present to allow either of these to occur. If not, then you can simply look uphill. Look higher on the roof for the source of the leak. What is directly above the spot where the water actually enters the house (the spot that you have determined by your attic inspection)?It is entirely possible that the leak is several feet or more higher up the roof than the point where water enters the house. For example, a hole in a shingle could allow water to penetrate the shingle, but the felt underlayment is intact and catches the water, allowing it to run downhill between the shingles and the felt until it comes to a place to penetrate the felt underlayment. Along the same lines (although it does not occur as frequently), water could penetrate both the shingle and the felt, but be caught by the plywood sheathing. It would therefore run beneath both the shingles and the underlayment down to the edge of the plywood, where it would finally enter the house. Standing at the point that you have determined to be the point of entry of the water into the house, look directly up the roof to see anything suspicious. If there is nothing obvious, such as an intrusion, a broken or cracked shingle, a missing tab, a loose vent screw or nail, a skylight, a chimney, or other such readily identifiable suspects, then begin to examine the shingles one at a time, starting at the point of entry. Using your flatbar, very carefully loosen each tab on the next shingle up by sliding it gently beneath each tab. Then, also very carefully, so as not to crack the tab where it flexes, lift the tab to look at the nail beneath it. Has the nail lifted? If soft sheathing or extreme flexion has allowed the nail to partially or fully withdraw, water could be entering through the nail hole. A drip leak has often been observed where the nail head has withdrawn less than a sixteenth of an inch. One clue that you are at the right place is a rusted nailhead. Commonly, galvanized roofing nails do not rust after installation of the shingles, since they do not get wet and they are sealed from water ambient in the air by the sticky-tab. So, if you see a rusted roofing nail in a shingle, be very alert to exactly what is causing it. It could be your leak.When you are considering the leak, always have as your base consideration the overview of the roof system itself: the elements that go together to make up the waterproofing medium. This means that in some instances you may wish to curtail your search for the leak in favor of advising the homeowner of the problem. For example, if all the shingles have lost their grit, have riverbedded or cracked, or are brittle and broken, then you will not be doing the homeowner a service by attempting a repair. Instead, immediately advise the homeowner of the condition of the roof and offer to cover it temporarily until it can be replaced. Sometimes the cause of a leak is so severe as to preclude, as a practical matter, a repair. The fix for some leaks, then, is roof replacement.Since the tile on top of the roof is not the waterproofing medium (the 90 lb. felt serves that function), then you cannot gain anything much from an inspection of the tiles and grout alone. Here, you go to the attic inspection that was discussed under Shingled Roofs to locate the point of entry, except that when you have located the point where the water is dripping into the attic, you have not pinpointed the leak. You have just narrowed down the area of tile that you will have to remove to find the cracked 90 lb. felt. This is because of the fact that in most cases the water penetrates the 90 lb. felt and proceeds downward on the underlayment until it reaches a breech in the underlayment. So we cannot really tell, most times, exactly where the 90 lb. failure occurs by identifying the drip point. We just know that it is somewhere uproof of that point. Again, we mark the uppermost drip point with a screw or nail through the roof, and further identify it with triangulation measurements, so as to reduce the work necessary to exactly locate the leak from above.On top, remove as few tiles as possible to allow you to see the problem area, remembering to always stay uproof of the drip point. If the 90 lb. is badly eroded or riverbedded, you may not be able to find the leak from a visual inspection alone. At that time you may have to go back into the attic, (now that the tiles have been removed in the problem area), and see if you can see light coming through anywhere. If that does not reveal the leak, then the garden hose is your next tool of choice. It really takes at least two people to properly use a garden hose in leak detection. One man should be stationed inside the attic just under the drip point. The second person on the roof starts with the end of the hose at the lowest possible point on the roof, and by making sideways, or horizontal strokes, should work his or her way with the running water very slowly, gradually, and methodically upwards. The person working the hose should not hurry this upward movement, or the observer in the attic may see the leak but not be able to pinpoint it. The observer, of course, should alert the roof person immediately when water enters, so that the roof person can know precisely where the water was falling at the first sign of the leak inside. So, very slow and steady does it. It is always best to anticipate that both the 90 lb. felt and the underlayment were installed all at the same time, and that if one section has become dry and brittle enough to crack, that the remainder of the roof almost certainly is in a similar state. So if you walk on, lift, handle, or otherwise disturb the 90 lb. or the underlayment, then it could easily cause further problems. In fact, an old roofer of some wisdom has stated that he will never attempt a repair on a tile roof, except when catastrophically caused. In other words, if strong winds knock off some tile and lift the felt, then it can be repaired, for example. But if a gradual deterioration of the 90 lb. and the underlayment has caused them to lose their elasticity and crack, then a new roof is probably in order. If you patch in new 90 lb. on an old tile roof, here is what can easily happen: the daytime expansion and the nighttime contraction of the 90 lb. felt caused by temperature fluctuations will cause particular stress adjacent to and around your patch, causing the cracks in that adjacent area of the old felt to open up, creating new leaks. This process will continue if you now patch in the new cracked area, literally moving around the roof. This is not only a waste of time, but it can also cause bad customer relations, because the customer believes that he has paid you to fix his leaking roof, and here it is leaking again in less that 90 days! He will probably feel that you should not charge him for the second and subsequent repairs, since he thinks that he has already paid you to fix the problem. And, from his perspective, he will probably think that you are not very good at your craft, since you have come back multiple times and still have not fixed the problem. So, a word to the wise is to make the customer aware of these facts before undertaking any repair on a tile roof. His best bet, ultimately, is to get new 90 lb. felt and underlayment over the entire roof. Even though this might be more expensive than a repair, it will be cheaper for him in the long run, since he will not have to pay for both repair work and the new roof that is actually needed. If, after considering all this, you still undertake a repair on old or brittle 90 lb. felt, then it is best if you can do the entire section of the roof where the leak has occurred. This will diminish your chances that you will have immediate subsequent leaks. Built-up roofs are often a real challenge in leak detection, even though in some cases they can be one of the easiest roof systems in which to find a leak. The reason for this split personality is that a visual inspection will often reveal the cause of a leak, but if your inspection does not make it readily apparent, then you may have a difficult task on your hands. You start by using the Science of Leak Detection. Most leaks on a built-up roof occur around the edges and around intrusions, of course. Where the water is entering will usually leave a discernable path where the water erodes the tar at the point of entry. Not only can it be worn down, but the tar will likely be discolored, too. (The tar can look brownish, rather than black, or, in some cases, have a whitish surface appearance). This means that it is fairly easy to see exactly where the water is entering sometimes. Also, readily apparent suspects present themselves in the form of cracked or pulled-away tar and holes of any kind, often showing some of the give-away signs just mentioned. One area that very frequently gives trouble is where the roof meets the wall, sometimes a few inches out onto the roof from the wall. The reason for this comes from the way that the underlayment was installed. If the membrane was not fitted tightly into the corner, or if supports were not used at the wall/roof junction, then there is an area that has a hollow space below it, right at the edge of the roof. This unsupported area is very prone to crack and break, causing leaks. Your initial visual inspection of the roof should always include a close and careful look at the wall perimeter. But what if your careful inspection shows nothing that would cause a leak? Before embarking on a laborious task of testing the components, it is time to employ the Art of Leak Detection. Remember to consider the roof system as a whole, thinking of how each of the components works with the others to create a waterproof system. For example, consider how the support members of this roof are constructed, as water will frequently travel along a support member. This can lead you to a deduction as to the general area of the leak, if not to pinpoint it. Narrow down your search by eliminating spots that have obviously never been wet. Then, think of all the elements of that particular roof that remain, and consider which of them is the most likely candidate. This allows you to establish priorities in proceeding. Then you can test each of these by the appropriate technique. But the time that you spend reflecting on how this particular roof is exactly constructed will almost always save you labor in testing components. Modified Bitumen. One of the easiest leaks to locate is in a modified bitumen roof. This is due to the fact that, if the roof was initially properly installed and has shown itself to be waterproof, then a failure of the seams is unlikely. And a failure around intrusions is not common. So that means that the cause of the leak is most probably a puncture. You simply look for the puncture. The only tricky part is if the puncture is hidden. For example, the corners of walkboards sometimes cause punctures. When someone steps on the corner, it angles down into the bitumen. But the walkboard covers this spot, so that an inspection of the bitumen is not possible without lifting the walkboard. Sometimes a leak is caused by someone stepping on a sharp object, puncturing the bitumen. This is usually seen, for instance, around air conditioner compressor units mounted on the roof. AC technicians who work on the units can step on a tool (or AC part, or any object with a sharp edge) that they have laid on the roof while working.   They probably will never even know that they have made a hole in the rubber, but it is there. Modified Bitumen. Other workmen who are on the roof can easily inadvertently cause a puncture in a modified bitumen roof. Fortunately, an inspection normally locates it. In the less common situation where the leak is a broken seam or an intrusion, we simply fall back on the systematic deductive techniques discussed earlier. General Rules. By now, you have probably discerned certain patterns in intelligent leak detection. You start with a broad overview of the particular roof system. Then you apply scientific practices of systematic elimination of causes that have previously been successfully employed for that type of roof. If that does not detect the leak, then you go to artful techniques. Just what those techniques will be depends in good part on the specific roof being examined, with the only permanent rule being: to be ever mindful of the components comprising that type of roof system. And, oh yeah: water usually runs downhill. Utilization of both scientific and artful techniques of leak detection will enable the professional roofer to detect a leak in the least time with the least work. To do this, the professional roofer must first understand the roof system that he/she is looking at, and know all its components and their function. They can then apply intelligent problem-solving techniques to the roof to produce a quick and reliable answer to the problem at hand.

Edited by Stephen Cutler on 5/31/2009 at 1:30 PM