How to Fully Shut Off Water to Your Tankless Water Heater

As a home improvement expert who has renovated dozens of bathrooms and kitchens, I‘m often asked how to safely turn off the water supply to a tankless water heater in order to make repairs or replace the unit. Properly shutting off water to your tankless heater keeps your plumbing protected and prevents leaks or flooding, but it does require methodically locating and turning off the right valves.

In this comprehensive guide, I‘ll walk you through the entire process step-by-step. I‘ll also share tips from my experience, troubleshooting advice, and alternatives to fully shutting off water based on the latest research and standards. Follow these best practices and you can successfully shut off water to your tankless heater.

Step 1: Locate and Close the Main Water Shutoff Valve

The first and most important step is to turn off the main water supply to your entire home or building. Here‘s how to find and shut off the main valve:

Identify the Main Valve Location

The main water shutoff is usually located in one of these places:

• Basement or utility room – Look for a large valve on the main interior water line.
• Garage – Check near the ceiling or along the backend wall.
• Crawl space – Access the crawl space and check near the front wall or foundation.
• Exterior of house – Most often it‘s near the front on the same side as your water meter.
• Near water meter – Some main valves are installed by the street meter.

Confirm It‘s the Main Valve

The main valve will typically be blue or red and labeled "main water shutoff." It will be the largest shutoff valve compared to others.

Turning off this main valve stops water supply to the entire property. Test by opening a faucet – if water stops flowing, you‘ve found the main shutoff.

Fully Close the Main Valve

Once located, turn the main valve clockwise until tight to shut off water to the home. I recommend using a valve wrench which provides maximum grip and leverage.

Turn slowly and gently. If you encounter resistance, don‘t force it. Penetrating oil can help loosen a stuck valve.

Once the main water supply is fully shut off, you can move on to isolating the tankless heater.

Step 2: Turn Off the Hot Water Supply Line

After shutting off water to the entire home, the next step is to turn off just the hot water supplying the tankless unit:

Locate Hot Water Shutoff Valve

Find the valve on the hot water line leading to the tankless heater. This is usually a gate or ball valve, and should be labeled "hot water shutoff."

It will be located between the main water line and the tankless unit. Check near other water heaters or on hot water lines.

Completely Close the Hot Water Valve

Once located, shut off the hot water supply to the tankless unit by turning the valve clockwise until tight.

At this point, only the cold water line will still be active. Shutting off hot water specifically prepares the tankless heater to be isolated.

Step 3: Shut Off Power to Tankless Unit

I can‘t emphasize enough how crucial this next step is. Before going any further:

Flip Electrical Breaker Off

Locate the circuit breaker for the tankless water heater in your home‘s breaker panel box. Double check it‘s the correct breaker, then switch it off.

This cuts power to the tankless heater and prevents the risk of dangerous electric shocks while servicing the unit.

Unplug Any Electrical Connections

Additionally, unplug any direct electrical connections to the tankless unit itself. This provides redundancy in case the breaker alone fails.

With both water and power shut off, it‘s safe to complete isolating the tankless heater‘s water supply.

Step 4: Shut Off Water Supply Lines at Unit

Now that main water and power are switched off, it‘s time to turn off the water lines connected to the tankless heater itself:

Close Inlet and Outlet Valves

Look for the water inlet and outlet pipes connected to the tankless heater. Use the built-in shutoff valves on the inlet and outlet lines to shut off water to the unit.

Slowly turn each valve clockwise until completely closed. These valves directly control flow to the tankless heater.

Check All Water Connections

Inspect all other water line connections to the heater and close any valves or shutoffs you find. Reference your owner‘s manual if needed.

This ensures no water can enter the isolated tankless unit. Once all valves are shut, the heater is cut off from the water supply.

Step 5: Release Pressure and Drain Remaining Water

Before servicing the tankless water heater, it‘s important to release pressure and drain any remaining water:

Open Pressure Relief Valve

Locate the pressure relief valve near the top of the tankless unit. Lift up the small lever and open the valve.

This safely releases built-up pressure and enables the unit to start draining.

Allow Unit to Fully Drain

Let the pressure relief valve run wide open until water stops flowing out. This evacuation process fully drains the tankless heater.

You may need a bucket to catch draining water. Now the unit is empty and prepared for maintenance.

Helpful Tips for Shutting Off a Tankless Heater

Based on my professional experience, here are my top tips for safely and successfully shutting off water to a tankless water heater:

• Consult manufacturer instructions for your specific make and model. Designs vary.
• Label each valve you shut off using masking tape and marker. This avoids confusion later.
• Turn valves gently and slowly to prevent damaging plumbing lines. Don‘t force!
• After closing main valve, check faucets to confirm water is fully shut off.
• Consider shutting off water to washing machine and dishwasher also if leaving for vacation.
• Completely drain tankless unit if shutting off for over 2 weeks to prevent stagnant water.
• Insulate exposed pipes with foam sleeves to slow heat loss if shutting off during winter.

By following each step carefully and methodically, you can completely isolate your tankless water heater from both water and power. This allows you to safely inspect, repair, or replace the unit as needed.

Troubleshooting Common Problems Shutting Off Water

During my years of plumbing repairs, I‘ve encountered a few tricky situations trying to shut off water to tankless heaters. Here‘s how I solved these common problems:

Valves Won‘t Turn

If valves are very old or infrequently operated, they can become stuck or seized. Here are some tips:

• Soak the valve overnight in penetrating oil to loosen rust.
• Tap the valve stem gently with a hammer to jar it free.
• Use a wrench or pliers to get more leverage on the valve stem.
• Twist slowly but firmly. Don‘t force it. Stuck valves may need replacement.

Water Continues Dripping

If you still notice water leaking from pipes or tankless unit:

• Double check valves are completely closed. Turn each one as far clockwise as possible.
• Partially closed valves must be forced completely shut or replaced.
• The tankless unit itself may be leaking internally if water keeps dripping after external valves are shut.

Missing Supply Shutoff Valves

No built-in shutoffs on water lines? Here are some workarounds:

• For inlet pipes without valves, install a gate or ball valve to control water flow.
• Unable to find any isolation valves? You may need to shut off main water to whole home temporarily.
• Add a hot water supply valve if missing – this allows shutting off just the tankless heater.

With some creative plumbing, you can add any missing valves needed to isolate your tankless heater.

Alternatives to Completely Turning Off Water

If shutting off your tankless heater entirely isn‘t practical, consider these alternative options:

Adjust to Low Temperature Setting

Instead of fully shutting off, simply adjust the temperature dial on the tankless unit to its minimum setting, around 100°F. This prevents stagnant water and reduces energy costs.

Install a Vacation Shutoff Switch

A remote vacation switch allows you to easily turn the tankless heater on and off without accessing valves. Flip it off when away.

Partially Close the Main Valve

If shutting off completely, partially close the main valve to reduce flow to a trickle. Only recommended very short-term.

Insulate Exposed Water Lines

Wrapping pipes in foam insulation sleeves maintains temperature longer if water is turned off. Helpful in winter.

While shutting off water completely is best for long vacations, these options reduce strain on the heater for short trips.

Answers to Common Tankless Water Heater Shutoff Questions

Let‘s review answers to some of the most frequently asked questions I get about shutting off tankless water heaters:

How long can my tankless stay off?

Fully drained tankless heaters can stay shut off for 1-2 months max before stagnation becomes a problem. Turn back on periodically for longer outages.

Is it safe to shut off just water and not power?

Never shut off water without also cutting power! Running the heating elements dry will destroy the heat exchanger.

Do I need to shut off gas too if it‘s gas-powered?

Yes, for a gas tankless unit, shut off the gas supply and turn the temperature dial down. This avoids any gas leaks.

What‘s the best temperature setting to leave it at?

When draining for vacation, set the unit to 100-110°F. This prevents bacteria growth in stagnant water.

How do I get it back up and running after?

Slowly open valves in reverse order from shutoff. Refill lines first, then restore gas/power once all leaks are checked.

Can pipes still freeze with water shut off?

Yes, pipes can still freeze without flowing water in winter. Take preventative measures like insulating exposed pipes.

Properly shutting off your tankless heater keeps your plumbing protected and prevents costly leaks or flooding. By following these professional tips and techniques step-by-step, you can successfully shut off water and power to your unit for maintenance or repairs. Let me know if you have any other tankless water heater questions!