Tankless Water Heater Maintenance and Winter Care

A tankless water heater needs less space than a tank. It does not need less attention. In New Hampshire, most of that attention comes down to scale, freezing and power.

Routine maintenance

• Descaling. Minerals in the water build up in the heat exchanger over time. Manufacturers call for periodic flushing, and how often depends on how hard your water is and how much hot water you use. Follow the schedule in your model's manual.
• Inlet filter. Most units have a small screen on the cold-water inlet that catches debris and needs occasional cleaning.
• Vent and intake. Keep vent terminals clear of snow, ice, leaves and nests, and keep the required clearances around them.
• Condensate drain. On condensing models, the drain line and any neutralizer need to stay clear.

Freeze protection needs power

Most tankless heaters protect themselves from freezing with small built-in electric heaters. Navien, for example, states that this protection requires electricity, and that the gas supply should stay on for added protection. ^[1]

That has two consequences:

• During a power outage, a tankless heater makes no hot water. Its controls, fan and ignition all need electricity.
• During a winter outage, the unit can be at risk of freezing. Manufacturers' instructions for prolonged power loss in freezing weather generally involve draining the unit, or a backup power source or drain-down accessory designed for the model. ^[1]

Freeze damage is commonly excluded from manufacturer warranties; Navien's limited warranty, for example, does not cover it. ^[1] If long outages are common where you live, plan for this at installation, not during the first storm.

Outdoor and cold-space installations

Outdoor-rated units exist, and they save indoor space. They also carry more freeze risk. Navien advises against installing its tankless heaters outdoors in areas prone to freezing temperatures. ^[1] If an outdoor or cold-space location is being considered, it should follow the specific manufacturer's cold-climate requirements, and indoor alternatives are worth comparing.

Indoors, a unit can still freeze if cold air comes down the vent or the space gets very cold during an outage. Condensate lines running through cold areas need protection too.

Common problems and what they usually mean

• Water turns lukewarm when a second tap opens. Demand has gone past what the unit delivers at that temperature rise, which is a sizing question. Winter makes it worse. See sizing.
• A brief burst of cold water between uses. Often called a "cold water sandwich": water left in the pipes cools, then the heater takes a moment to fire again. Recirculation or a small buffer can reduce it.
• Slowly falling output or error codes over months. Commonly scale building up in the heat exchanger, or a clogged inlet filter.
• The unit shuts down in cold weather. Can point to a frozen or blocked condensate drain, a blocked vent, or freezing. Check the manual for the error code, and stop using it until it has been checked.
• Very low flow at every tap. Can be a clogged inlet filter.

If an error code involves the gas supply, venting or combustion, have it looked at before running the unit again.

Want a heater sized and installed with winter in mind? Request an estimate or call us.