FAQs

Scale in the heat exchanger, followed by ignition faults and flow sensor or filter problems. All three usually show up as a code or as water that won't stay hot.

A brief cold slug after a tap reopens is the unit restarting. Swings during one shower usually mean flow below the unit's minimum, scale on the exchanger, or a failing flow sensor.

Check for power at the outlet and that the gas valve is open. Beyond that it is usually low flow, a clogged inlet filter, a failed flow sensor or an ignition fault.

On Rinnai, Noritz and Rheem units, 11 means no ignition. Gas supply, gas pressure, the igniter, the flame rod and the venting are the usual suspects. Navien's version is E003; Takagi's is 111.

On Rinnai and Noritz units it points to an air supply or exhaust problem: a blocked vent, a nest, snow at the termination or a vent run that's too long. Navien uses E110 for venting faults.

Most units reset by switching power off and on, or through the controller. A reset clears the code, not the cause; ignition and exhaust codes that return need a repair visit.

Most makers call for a flush every year, and every six months on very hard water. On very soft water the gap can be longer, but skipping it for years invites scale faults.

Many owners do, with a small pump, hoses and a bucket on the service valves. Units without those valves need them added first, and a descale won't fix a failed part.

Keep the power on so freeze protection can work, close the unit's water valves if a line has split, and warm exposed pipes gently. Have the unit checked before running it hard.

Yes, in most cases. Igniters, flame rods, flow sensors, thermistors, fans, gas valves and boards are all replaceable, and scale can be descaled. A leaking heat exchanger on an old unit is the main exception.

Gas units commonly run 20 years or more when they are flushed on schedule. Electric tankless units tend to last closer to 7 to 10 years.

Most part repairs are estimated at $150 to $800. Descaling is estimated at $150 to $350, and a heat exchanger replacement at $1,000 to $2,500.

Often, when the unit is young or the exchanger is still under its parts warranty. On a unit past 15 years, a new heater can be the better spend; you'll be told which.