Water heater TPR discharge reduced on a closed system without expansion tank
A 50-gallon gas-fired water heater in an attached garage is 12 years old and has a standing pilot. It sits directly on the garage floor, and the garage has a step down from the house. The TPR valve has a discharge pipe that runs 15 feet with three elbows, is reduced from 3/4 inch to 1/2 inch, and terminates outside 24 inches above grade with a threaded end. There is a backflow preventer on the main water line and no expansion tank. The homeowner reports the TPR has been dripping for about a month and has placed a bucket under the pipe inside the garage, although the pipe exits outside. There are water stains on the floor near the heater. The water heater's label shows a 150 psi maximum working pressure and a 210-degree Fahrenheit TPR rating.
1. Identify the defects and the sequence of failure that could occur.
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The TPR discharge is reduced from 3/4 inch to 1/2 inch and has a threaded end; that restricts the required full-size relief flow and the threaded end could be capped. The pipe terminates outside 24 inches above grade, where it can freeze or be blocked, and the long run with elbows adds resistance. The closed system has a backflow preventer and no expansion tank, so thermal expansion during heating has nowhere to go and raises pressure. The TPR may drip as it relieves that pressure, which is a warning, not a nuisance. If the TPR is capped or blocked, pressure can continue to rise until the tank or a fitting fails. Separately, a 12-year-old gas water heater with a standing pilot sitting on the garage floor is an ignition risk; many installations require elevation or a flammable-vapor-ignition-resistant design. The sequence is: closed system plus heating causes pressure rise; the TPR relieves; a reduced or blocked discharge makes relief ineffective; tank rupture or scalding risk follows.
2. What do you recommend and what should you not do?
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Recommend a licensed plumber install an expansion tank or other approved thermal-expansion control, replace the TPR discharge with full-size pipe, remove the threaded end, and terminate at a safe location that cannot be blocked or frozen. Recommend correcting the water heater elevation or verifying the FVIR rating, and checking the TPR valve itself. I would not cap the TPR, not plug the drip, and not test the TPR by lifting the lever if doing so could cause a leak I cannot control; follow your inspection standard and the manufacturer. I would report the dripping TPR and the reduced discharge as safety hazards, not as a maintenance item. If the tank shows heavy rust or the TPR is stuck, recommend replacement rather than repair. The client should not rely on the TPR as the only safety device.
3. The buyer says a home warranty will cover the water heater if it fails, so they will skip repairs. How do you frame the risk?
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A home warranty is a service contract, not a safety device. It may replace a failed tank after a deductible, but it does not prevent a pressure explosion, scalding, or water damage, and it may exclude improperly installed relief piping. The TPR and discharge are the last line of protection; reducing or blocking them defeats that protection. I would explain that the dripping TPR is telling us the system is already relieving pressure, and the fix is expansion control plus correct discharge. I would put the recommendation in the report and recommend correction before occupancy. If the client declines, I would document that the risk was explained and that they chose not to act. That is not a guarantee against liability, but it is honest and professional.