Abstract: An apparatus for heating liquid in a pipe to prevent freezing of the liquid and for de-icing of frozen pipes includes an elongated housing constructed of plastic material and having a central bore and fittings for detachably coupling each end of the housing to the open end of a liquid pipe so that the central bore connects a first liquid pipe to a second liquid pipe. The fittings each comprise a sleeve attachable to the pipe end, a sealing gasket between the end of the housing and an annular flange on the sleeve, and a threaded coupling nut cooperating with external threads on the housing and having a flange engaging the sleeve flange. The housing includes a lateral passageway intermediate its end communicating with the central bore and closed by a sealer valve having an opening with a normally closed penetrable seal of elastomeric material.