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Question DetailsAsked on 2/1/2018

why is water slow dripping out of white pvc pipe on side of hot water heater into the drip pan under it?

The hot water heater is 3 years old.

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1 Answer


OK- if this pipe comes off the temperature and pressure valve - which looks like this and comes off the side of the water heater tank near the top and should have a pipe down from it to within a few inches of the floor -

then the T&P valve is leaking, or your water heater is pressuring up because there is a backflow/pressure regulator device in your system so as the water heats it expands and cannot go anywhere, so it oozes out the overpressure valve. In some cases, an increase in household water pressure - due to failing pressure regulator, change of well pump or sometimes even q major increaseof water level in a deep well, or due to utility increasing pressure for fire fighting or such, can cause weeping TPV valve - especially about about 70-80 psi.

In the first case, exercising the valve using the lever on it (which should be done annually - and beware the hot water coming out) might make it reseal again, but may also cause more of a leak.

In the latter case, if there is a pressure regulator or backflow preventer or similar device on the incoming water lines which prevents backflow during expansion of the hot water, then an expansion tank needs to be installed. Lots of previous questions with answers about water heater expansion tanks can be found in the Home > Plumbing link, under Browse Projects, at lower left.

If this has not done this before, more likely the first than the latter cause.

BTW - if white PVC (as opposed to CPVC, which is most beige or off-white) then that is not to code - has to be pipe rated for hot water service, commonly copper or CPVC, same diameter as TPV valve outlet (commonly 3/4" in residences).


Second possible case - if this pipe comes off the exhaust flue - usually PVC but sometimes stainless pipe or duct, usually 2-3 inch on normal residential sized units, coming off the top (centered except if you have a heat pump on top) of the water heater and leading outside, meaning you have a high efficiency "direct vent" rather than "gravity vent" heater, then this is condensation from the flue gases. The colder the weather or ambient temperature around the heater, the more of the moisture in the combustion gases condenses in the piping, and in some systems there is a drain pipe or tubing (commonly about 1/2") to collect any condensation accumulating in the flue near the heater and drain it away. In proper installation, as much of the flue pipe as possible drains to the outside, and many that rise straight up and then slope downhill all the way to the outside do not have a condenation drain.

If this is what is happening, would be considered normal - especially in cold ambient conditions. The drain vent commonly looks like below link in the flue pipe (which may be stainless steel or plastic) - also occasionally used on gravity flues which are external to the building or pass through unheated space, to collect condensation from the flue pipe and drain it off so it does not drain down into and rust out the water heater.

One other thought - the TPV valve and the condensate should NOT lead into the catch pan, because drainage or test water from them will flood the bottom of the water heater (unless it was blocked up) and eventually rust it out if not plastic, but either way can flood the burner and pilot and any air vent on the bottom as well as some sensors low down in the firebox, plus rust out the water heater housing. They should be routed to drain OUTSIDE the pan, hopefully to a floor drain or similar place which will not cause trouble or damage. Details here -

If that does not help or fully answer your question, google for blogs/artilces on wter heater TPV valve or condensate drain, as applicable.

If you decide you need a tech to look at this, Heating and A/C would be the Search the List category to find well-rated and reviewed ones.

Answered 2 years ago by LCD

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