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.

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