Rinnai Tankless Flush Fix: Stop Wasting Water NOW!

Understanding and Fixing the Rinnai Tankless Flush

A "Rinnai tankless flush" – or what’s sometimes also called "cold water sandwich" – refers to the initial burst of cold water that can occur when activating a hot water tap connected to a Rinnai tankless water heater. This happens because the hot water heater needs a moment to fire up and heat the water within its coils, and that initial cold water is the remnant left in the pipes between the unit and the faucet from the last time hot water was used. This can be a frustrating experience and waste water. This article details how to understand, diagnose, and potentially fix this issue.

Identifying and Understanding the Rinnai Tankless Flush Problem

What exactly is the Rinnai tankless flush?

The "flush" is the period when cold water is delivered before hot water starts flowing from your tap or shower. It’s more noticeable with tankless water heaters than traditional tank heaters because tank heaters always have hot water readily available in their tank. Rinnai tankless heaters only heat water on demand, so there’s a brief delay.

Why does this happen?

• Distance: The further the faucet is from the Rinnai unit, the longer the flush will last, as the cold water has a greater distance to travel before the hot water arrives.
• Pipe Insulation: Uninsulated pipes will allow the water within them to cool down faster, leading to a longer flush.
• Activation Delay: Tankless water heaters need to detect a certain flow rate before they begin heating water. If your flow rate is borderline, it can contribute to a longer cold water flush.
• Minimum Activation Flow Rate: Every Rinnai model has a minimum flow rate that it needs to sense to activate. If the flow at your faucet falls below this, the unit will not heat.

Is the flush normal?

A small flush of cold water is normal, especially if the faucet is far from the heater. However, an excessively long flush (more than a minute or two) indicates a potential problem.

Troubleshooting Steps for Rinnai Tankless Flush

Check the Water Heater Settings

• Temperature Setting: Verify that the water heater is set to a reasonable temperature (e.g., 120-130°F). An excessively high setting could exacerbate the cold water flush issue as the heater needs more time to reach the desired temperature.
• Eco Mode: Some Rinnai models have an eco mode which can delay the heater firing up in an attempt to save energy. Disabling this mode may reduce the flush, but might also increase energy consumption. Consult your Rinnai manual for how to adjust this setting.

Assess Pipe Insulation

• Inspect Exposed Pipes: Look for exposed hot water pipes, especially in unheated areas like basements or crawl spaces.
• Insulate Pipes: Insulating these pipes can drastically reduce heat loss and shorten the cold water flush. Use foam pipe insulation sleeves, readily available at hardware stores.
• Evaluate Pipe Runs: Consider shorter, more direct pipe runs to faucets. The longer the pipe, the more heat it can lose.

Evaluate Flow Rates

• Measure Flow Rate: Using a measuring cup and a timer, determine the flow rate at the affected faucet. Open the faucet fully for a set time (e.g., 10 seconds), then measure the water collected. Multiply to determine the flow rate in gallons per minute (GPM).
• Compare to Minimum Flow Rate: Check your Rinnai model’s specification sheet for the minimum activation flow rate. If your faucet flow rate is consistently below this value, the heater may not be activating reliably, resulting in a long flush.
• Check Aerators and Showerheads: Low-flow aerators or showerheads can restrict water flow, potentially causing issues with the minimum activation flow rate. Consider removing or replacing them with models that provide a higher flow rate. However, balance this with water conservation.

Consider a Recirculation System

A recirculation system actively circulates hot water through your plumbing lines, ensuring hot water is always readily available at the tap. This virtually eliminates the cold water flush.

• Types of Recirculation Systems:

  • Dedicated Return Line: Requires a separate plumbing line running from the furthest fixture back to the water heater. This is the most efficient type but is best installed during new construction or a major renovation.
  • Comfort Valve System: Uses the existing cold water line as a return line. A valve installed under the sink connects the hot and cold water lines, allowing the water to circulate. This is easier to install in existing homes.
  • External Recirculation Pumps: Attach to the existing hot and cold water lines directly at the water heater, circulating the hot water without needing new plumbing.

• Cost and Complexity: Recirculation systems vary in cost and complexity of installation. Consider your budget and plumbing skill level when choosing a system. Professional installation is recommended for complex systems.

Rinnai Maintenance and Professional Check-up

Routine Maintenance

• Flush the Heater: Regularly flush the water heater to remove mineral buildup. This buildup can reduce efficiency and potentially affect the heater’s ability to activate quickly. Consult your Rinnai manual for specific flushing instructions.
• Air Filter: Check and clean the air filter regularly (if your model has one). A clogged air filter can restrict airflow and reduce efficiency.

When to Call a Professional

• Persistent Issues: If you’ve tried the above steps and the cold water flush persists, it’s best to call a qualified plumber or Rinnai-certified technician.
• Complex Plumbing Modifications: Installing a recirculation system or making major plumbing modifications is best left to professionals.
• Gas-Related Issues: Never attempt to repair or modify the gas connections to your water heater. This is a job for a licensed gas fitter.
• Error Codes: If your Rinnai unit is displaying error codes, consult the manual or contact a professional for diagnosis and repair.

So there you have it! Armed with this info, you’re well on your way to tackling that pesky rinnai tankless flush issue and stopping that water waste. Happy flushing (in a good way, of course!).