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Q.I have a leak in my recently installed radiant tubing, no doubt caused by freezing last winter before the system was fully operational. The tubing is a 300-foot run buried in a 4-inch concrete slab. Is there some kind of "stop leak" that can be circulated in the system to plug the leak? Is there a way to locate the leak?

A.John Siegenthaler, a consulting engineer specializing in hydronic heating system design in Holland Patent, N.Y., responds: As far as I know, there's no product that can be circulated through any type of radiant tubing that will stop a leak. So you'll have to cut out the damaged tubing and splice in a new section.

First, though, you have to find the leak. The only reliable method I know is to run warm water through the system and view the slab with a thermal imaging camera; the leak will appear as a plume spreading out from the tubing. This will work best if the slab is relatively cool when the test is initiated.

Once you've located the leak, mark the location on the slab, chip away the concrete to expose the tubing, and patch the leak. Check with the tubing manufacturer for the required fittings and procedure to do the repair, and be sure to pressure-test the circuit before patching the slab.

The hardest part of this process may be locating a thermal imaging camera. Unless you have access to one owned by a local utility, volunteer fire department, or other agency, you'll need to contract with an infrared inspection service.