condensation corrosion
Yes, the tankless water heaters do cost more than the normal water heaters because tankless water heaters are designed to supply hot water only when needed unlike normal ones.
Most hot water heaters will develop small leaks around the welds in 10-12 years. Heaters are made of much thinner, cheaper material than they used to be. -The actual wall thickness of a typical water heater today is 1/16 inch, and no interior protection against rusting.
American Water Heaters.
American Water Heaters
Electric water heaters have not carbon monoxide.
You can buy water heaters from any home hardware store.
GE hot water heaters are made by Rheem.
Rheem provide a series of high efficiency gas water heaters. Several different companies also provide tank-less water heaters, which are very efficient, as well as solar water heaters.
Natural gas water heaters utilize a single burner to heat up to 65 gallons of water, depending on the size of the tank. Water heaters are fairly durable and can provide years of trouble-free service. Over time, however, gas water heaters can develop leaks an other internal problems. Many problems can be repaired, but the costs of repairs can eventually exceed the cost of simply replacing the water heater. Thankfully, replacing a natural gas water heater is a straightforward process.
"Rheem does manufacture both gas and electric water heaters. Rheem currently offers 18 different varieties of gas water heaters and 9 different varieties of electric water heaters. Both types of Rheem water heaters are known for their rigorous standards, reliability, and efficiency."
Water heaters can range from 1 unit to 10 units.
Possibly the boiler is firing oil and thus the soot from the oil is spilling back into the gas flue