Water heater leaking from the bottom: what it means and what to do

A tank water heater is a steel cylinder with a glass lining and a sacrificial anode rod that corrodes instead of the tank. Once the anode is used up and sediment builds up on the bottom, the tank itself starts to rust from the inside. The first sign is often a slow drip or a puddle at the base. In many Ontario homes the tank is rented from a water heater rental company rather than owned, which changes who you call first.

Why is my water heater leaking from the bottom?

Water at the base does not always come from the base. Dry the tank and the floor with a towel, then watch where the water reappears. The table sorts the common sources by what you see.

What should I do right now?

1. Turn off the heat source. On a gas water heater, turn the gas control knob to OFF, or close the gas shut-off valve on the pipe to the heater. On an electric heater, switch off its breaker in the panel. A power-vented gas heater also has a plug; unplug it.
2. Close the cold water supply valve on the pipe going into the top of the tank.
3. If water is still coming out and there is a floor drain nearby, you can drain the tank: attach a garden hose to the drain valve, run it to the floor drain, open a hot tap upstairs to let air in, then open the drain valve. The water can be hot enough to scald, so let it cool first if you can wait.
4. Take photos of the leak and the label on the tank. The label shows the model, the serial number, and often the owner if it is a rental.
5. Move stored boxes away and put a pan or towels down to protect finished floors.

Is my water heater rented, and who do I call?

Check the tank for a sticker from a rental company, and look at your gas or utility bill or bank statements for a monthly water heater rental charge. If the tank is rented, it belongs to the rental company. Call them first: under a typical rental agreement they repair or replace their own equipment, and a plumber you hire cannot usually remove it. RedFlagDeals threads from Ontario homeowners show how much the details vary, from a free drain valve swap to questions about whether a replacement starts a new contract. Read your agreement for what happens when a tank is replaced or removed, and ask the company in writing. If the money involved is significant, a consumer protection lawyer or Consumer Protection Ontario can explain your rights.

If you own the tank, a licensed plumber can fix a leaking valve or fitting, or quote a replacement. Plumbing is a compulsory trade in Ontario, so the plumber should hold a Certificate of Qualification (306A). A gas water heater is also a gas appliance: connecting a new one must be done by a Technical Standards and Safety Authority (TSSA) registered fuels contractor with a certified gas technician, and some replacements need a municipal plumbing permit.

Can a leaking water heater tank be repaired?

No, not when the tank itself is leaking. Once the steel shell has rusted through, the leak will grow, and patching the outside does not stop the corrosion inside. What can be fixed is everything attached to the tank: the drain valve, the relief valve, the supply connections and the anode fitting. That is why finding the exact source matters. A worn drain valve is a small repair; a wet, rusty base is a replacement.

Why is the relief valve on my water heater leaking?

The temperature and pressure relief valve opens when the water inside is too hot or the pressure is too high, and a little water from its discharge pipe is the valve doing its job. If it drips often, the thermostat may be set too high, the valve may be worn, or the house may have a thermal expansion problem. Homes with a backflow preventer or a pressure-reducing valve on the water service form a closed system, and a tank that heats water has nowhere for the expanding water to go, unless there is an expansion tank. A plumber can test the house water pressure and check whether an expansion tank is needed.

What does a plumber cost on Doyo for this?

Doyo does not list water heater replacement as a job. For an owned tank with a leaking valve, fitting or pipe, Doyo's Pipe Repair job sends a licensed plumber (306A), and it is priced by written quote: the call-out fee is credited against the repair, and you get a diagnosis and a written price before anything is cut. Doyo checks the plumber's Certificate of Qualification before they are offered plumbing work. For a rented tank, call the rental company first.