In the radiant business we often hear prospective customers ask. What happens when you get a leak? After several years in this business, we know that tubing failures are very rare, and can always be blamed on damage during installation or damage created later by a outside force such as a nail or screw.
Preventing damage to the tubing in an existing slab is best attained by putting up the warning signs, making sub-contractors aware of the tubing and by keeping the tubing in the bottom of the slab.
Although we often dread the thought of trying to locate and repair problems in slabs, in actual practice they are relatively easy to locate and repair. A low return water temperature in one loop often is caused by a blocked tube. If this is a new problem in an old system, it should be either sediment or rust. Sediment can usually be removed by disconnecting the loop and back flushing with high pressure water or air. Rust will sometimes attach itself to the wall of the tubing and need to be chemically flushed.
If it is a new system the problem could be a pebble or dirt which can be flushed out by back flushing with high pressure water or air. The most common problem is tubing that is kinked during the concrete pour. Disconnecting the loop and running high pressure water or air through it, you can locate the problem by the sound it makes. A stethoscope will pin point the kink. Using a roto-hammer you can break a small hole (usually about 12 inches in diameter), splice the tubing, and mix up sand and cement in a bucket and repair the hole. Be sure to use a brass coupling and wrap it to protect it from the concrete.
Another method is to run a fish tape down the tube and put a signal on it and follow it with a locator.
The best tool for trouble shooting that I have found, is an infrared thermometer that sells for less than $200.00. This tool is extremely accurate for locating tubing in any floor and really shines when you try to locate leaks in slabs.
The best method that works for me to find a leak in a slab is to let the slab cool down, then turn the loop on that leaks. Keep the boiler hot. Holding the scanner a couple of inches above the floor, follow the supply line out from the boiler. If you scan this area carefully as it heats up, you can pinpoint the leak and see the plume as the water spreads out under the slab. As you swing the scanner back and forth over the tube you will see a spike directly over the tube, when you get to the leak you will see this spike begin to disappear as the heat spreads out.