Rinnai tankless water heater goes cold

Rinnai tankless water heater goes cold. Rinnai tankless water heaters are efficient and durable until they get defected like a water heater goes cold.

It’s a very annoying situation when morning you go for a shower and the water accidentally gets cold. There are very reasons that cause the heater to go cold.

The first reason could be the improper gas line sizes, heater work with the gas, and required compatible size pipelines.

If the line is ok, there could be a problem with the water filter, when the cold-water filters get a blockage, you may face the situation of cold water in the shower or faucets. Sometimes there happens cold water sandwich which occurs due to turning off and on the water tap.

Rinnai tankless water heater goes coldRinnai tankless water heater

Rinnai tankless water heater can go cold because of many reasons, such as the broken or faulty flow sensor. Besides that improper installation and dirty water filters are also among common reasons. The clogged heat exchanger can cause the water heater to go cold.

Improper gas line size

Rinnai tankless water heaters provide efficient performance with natural gas or liquid propane. In ideal cases, you are recommended to extend the gas line for your tankless water heater.

Mostly gas lines are ½ or ¾ and they are good with Rinnai water heaters but tankless 1 is more prominent.

When the gas line size is not compatible with the Rinnai Tankless heaters it can cause incomplete combustion resulting in equipment failure.

A clogged or dirty water filter in a cold water inlet

The water filter is a small plastic item that performs the job of filtering cold water entering the heater. Its located at the bottom of the heater and filter water supply.

Over time the filter can get dirty or clogged because of the unwanted particles. If the water filter gets clogged, no cold water enters the heater and as results, you will not have any hot water.

Coldwater sandwich

A cold-water sandwich is one of the common problems for Tankless water heaters at your home. Coldwater sandwich is Temperature fluctuations in the tankless water heater system.

When there is a cold water sandwich your heater system provides hot water and the next minute you will get cold water, and then again hot water. That’s a very frustrating situation in the morning shower.

Rinnai tankless water heaters are designed to conserve energy, which means they work on the principle of energy conservation. When you turn off the hot water tap, the heater also turns off.

When you turn off the tap, heaters also turn off and it will get cold water. When you again turn on the water tap, the heater turns on but gets some od cold water from the pipes.

Clogged heat exchanger

Heat exchangers are internal components of the water heater. These are small pipes that are responsible to change the state of water from cold to hot using heat.

But when the heat exchanger gets clogged, you may face the problem heater is not working. Heat exchangers clogging occurs due to minerals in the water, water from well contains minerals, hard water deposits minerals in pipes and clogging happens.


Tankless water heaters are intelligent water heating systems. They are very effective unless any problem occurs. The earlier mentioned reasons are the most common one due to which a water heater goes off. Keeping the filter clean, and properly servicing the heater helps to keep it running.

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