Exploring Tankless Water Heater Parts
Buying, Replacing & Installing Tips
(updated 2018)

Tankless water heater

The article about tankless water heater parts explains the main components of the electric and gas water heating appliances that heat water on demand.

We will cover the top manufacturers of on-demand models, including AO Smith, Rheem, Paloma, Rinnai, Bosch, Noritz, and others.

An article about tankless water heater parts is to help you in your home DIY project such as troubleshooting, servicing, repairing and when replacing the broken parts. As described before, in the article about tankless water heaters, tankless technology allows water to be heated on demand and delivered instantly.

This new and innovative technology works differently from the storage tank heaters. The great advantage of tankless over tank type models is that majority of the parts are replaceable and recyclable. And because of that, and to save money, it is good to know about each component, and how to replace it.

Main tankless water heater parts

  • Heat exchanger
  • Gas valve 
  • Burner
  • Ignition system
  • Combustion chamber
  • Combustion fan
  • Temperature sensors
  • Safety elements
  • Venting
  • Electronic system
  • Water valve
  • Remote controller

Keep in mind that above tankless water heater parts are not all present on different brands and models; our goal is to cover a majority of the important elements found among different manufacturers.

Heat exchanger

The heat exchanger is a device, made of copper tube, or stainless steel, where a small quantity of water is stored – passing through, and used to transfer the heat from the gas burner. The heat is generated from the gas on the gas burner that is burning below the heat exchanger. In a case of the copper heat exchanger, the copper tube is combined with the copper fines, to increase the overall surface and increase the heat transfer.

In electric water heaters, water is heated by a heating element (i.e. electric coils) which is turned ON by a flow activated switch.

The advanced tankless water heaters, like Rinnai, have a commercial grade heat exchanger which is more durable and efficient. Noritz has a superheat exchanger with a thicker piping for longer life and increased thermal efficiency. Condensing water heaters, due to the acidic nature of the condensate, are equipped with the stainless steel heat exchanger.

In winter, when the heat exchanger is not used, cold water inside might freeze, especially when the cold air comes down through the vent pipe. This is why a minimum length of the vent pipe and combustion air is required.

Due to the high mineral content in water, the heat exchanger may be scaled internally so the proper maintenance is necessary.

Most of the manufacturers will provide a warranty on heat exchanger, which can be from 12 to 15 years while on other tankless water heater parts, the warranty is usually one year.

Combustion elements

The combustion chamber is where the gas burns. A combustion chamber is designed as the room-sealed chamber (direct water heaters) and open (on atmospheric models).

Gas valves can be multi-stage and single-stage devices, with the modulation and ON/OFF option.

Gas valves with the modulation are adjusting its power based on the water flow, demand and changes in any incoming and outgoing water temperatures; ON/OFF works with the maximum or no gas power only.

Combustion fan is positioned below the burner so the air can be rapidly mixed with the burning gas resulting in an increased efficiency.

Burner elements

The gas burner is usually installed below the heat exchanger, and on some commercial and condensing water heater models are made of high quality, stainless steel material, so it can work with higher heat outputs. Some manufacturers are designing high efficiency and high power burners like Ceramat burner from Bosch and Aquastar units.

Noritz water heaters are using a dual-flame technology to maximize the output, provide temperature stability and keep the gas emission low.

With other manufacturers, you can see a huge progress toward the environmentally friendly burners, burners designed to reduce the NOx emission.

The burner flames that are generated on the burner should have a blue color, while yellow flames are a sign of a wrong orifice size, dirty burner or blockage of the heat exchanger fins and improper combustion.

It is recommended to check the shape, pattern, and color of the burner flame through the provided sight window located at the front of the heater's cover.

Ignition system

The ignition system is using either a pilot light with the thermocouple – which is rare or electronic ignition device, usually with one or two electrodes. Both systems are used to light the fire on the main gas burner and inform the control device that the flame is either on or off.

Bosch has a great innovative design where the water heaters are equipped with the hydro-generated ignition system that allows this tankless water heater to operate without a pilot light, electricity, or a battery.

Safety features

Every tankless water heater is equipped with the safety and control elements that are working together with the PC board for better protection, safety, and performance.

  • Flame sensors or ionization rods are used to ensure that the flame is present, which secure the proper water heater work. When the flame is extinguished/gone it sends the signal to stop the gas flow and the water heater will shut down. The thermocouple is used on models with the pilot light.
  • Overheat sensor will trip due to overheating, shutting the unit down. If the hot water temperature exceeds the predetermined value, the unit must cool down before resuming the operation.
  • Temperature limiter and frost/freeze sensor protect the water heater from freezing.
  • Fan speed monitoring is used to ensure the proper fan operation.
  • Water flow sensor protects the system from the minimum flow, so the heat exchanger can get enough water for normal operation.
  • Pressure relief valve is used to protect the heating system from the excessive water pressure in the system.

Control panel

A PC electronic board is the most sophisticated among tankless water heater parts and is the heart of the water heater. It is used to provide the diagnostics; it reads and displays the temperature and error codes on the LCD display, and using an onboard memory chip to store the code for easy maintenance and troubleshooting.

This self-diagnostic computer system and intelligent electronic controls are also designed to increase energy efficiency and safety, also working toward reducing the NOx gases.

Venting

Tankless water heaters using gas are designed to vent the gases out and bring the air in using one of the three options:

  • Direct Vent
  • Power Vent
  • Atmospheric Vent

Note: The installation of venting must comply with the national and local codes and per manufacturer's instructions (to meet the minimum and maximum lengths, location, recommended distances).

Venting pipes can be run horizontally through the side wall or vertically through the roof, with the two-pipe system or concentric venting.

A condensate collector must be used on all vertical installations, while on horizontal runs downward slope should be provided.

The air intake pipe can use aluminum, ABS, CPVC or PVC pipe, while for combustibles, UL approved, Category III, stainless steel vent material must be used.

Ordering tips

For placing an order for any of the tankless water heater parts contact a store where the water heater was purchased, manufacturer or the distributor providing the following information:

  • Include the model and a serial number of your tankless water heater found on the rating plate.
  • Include the gas type (natural gas or propane gas - LP).
  • Include the part description and number of required parts.