Water heater condensation is not a leaking problem. Condensation is normal occurrence when the gas water heating appliance is working. How to recognize condensation in water heaters, what to do, can it be stopped and how to troubleshoot problems?
When natural or propane gas burns in gas water heaters, a lot of moisture in products of combustion is released. So when the water vapor is chilled below the dew point (link wiki), water heater condensation occurs. The dew point is the temperature at which water vapor turns into the liquid state, called condensate.
When the main gas burner is on, the heater produces hot flue gases, which turn into the condensate upon contacting colder surfaces. One of the situations where the condensation might happen is piping cooled by the low incoming water temperature that flows through.
In order to troubleshoot the water heater condensation you have to recognize the symptoms first and which part of the unit condensates. Below are the main reasons for condensation:
Because of the suddenness and the amount of condensate, this problem might be diagnosed as the leaking. Keep in mind that one half of the gallon of condensate during every hour of operation is a typical for home heaters. It takes 1-2 hours for the tank to warm up so the condensation should disappear.
Since the new high efficient heaters and Energy Star models utilize the powerful gas burners; and combining it with the latest technology to extract even more heat from the flues and flames, they will condensate more than the older heaters that use less energy.
One of the solution when troubleshooting condensation in the heater is a good venting so the gas appliances will operate efficiently and vent the products of combustion together with the water vapor properly.
As the cooler flue gases are part of the reason for the condensation problem, the suggestion is to raise the supply air temperature, increase the stored water temperature or increase the size of the tank.
A suitable metal drain pan, at least 2" wider than the heater should be installed under the heater to collect the condensate and not to damage the area.
Condensing water heaters such as tank-type model Vertex from AO Smith, or tankless type from Rinnai, Noritz or Navien, produce the condensate that is acidic by nature (pH level is 2-3) and can cause the corrosion or damages to the drain and sewer system.
By buying the neutralizer kit and installing it on the water heater the condensate is properly treated for a safe disposal into the drain. The drain should be close to the unit, the pipe should provide a slope for a free flow, or, if it is needed, have the condensate pump installed.
Ensure that the condensate flow is free and clear of debris and the drain will not allow backflow through the hose. If the condensate backups into the water heater, an error code will flash, for example, a code "29" on Noritz NRCP model. This is important, especially during the winter and freezing days.
Almost all water heaters have some sort of condensation, if not due to an improper unit work than due to an increased moisture in the air. And controlling the moisture is not an easy solution. In a case of normal condensation, it is better to accept the fact. I would call a plumber only if there is an excessive condensation as it might cause premature tank corrosion and corrosion of heating elements and contacts.