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To flush a gas water heater, follow the exact manual for your model: turn off its gas heat source, cool the water, drain and flush the tank through a hose, then refill it completely and purge air before relighting. Gas controls and flushing methods differ by model, so do not substitute a generic sequence for the heater’s instructions.
Before you start
Find the heater’s make and model, then read its maintenance and lighting instructions. Whirlpool notes that its online guidance supplements the printed owner’s manual; follow the appliance labels and manual for your unit.
- A garden hose that fits the drain valve, routed to a suitable drain or safe outdoor location.
- A safe way to keep people away from hot discharge and prevent water damage.
Do not begin if you cannot identify the correct gas shutoff procedure, the drain valve is leaking, or the manual is unavailable and you are unsure how to proceed. Contact a qualified plumber or water-heater technician.
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How to drain and flush the tank
- Turn off the gas heat source as specified in the manual. A. O. Smith’s cited residential gas manual specifies the manual gas shutoff valve, but control layouts and instructions vary. Do not assume every heater uses the same control action.
- Cool the water. Open a nearby hot-water faucet and let it run until the water is no longer hot. Hot tank water and drain discharge can scald.
- Close the cold-water inlet to the heater. Connect a garden hose to the drain valve and route the other end to a suitable drain or safe exterior location. Make sure hot discharge cannot reach people or damage property.
- Open the drain valve. Opening a hot-water faucet helps air enter the tank and can speed draining. Drain the tank as directed by its manual.
- Flush according to the model-specific method. Continue until sediment no longer drains or the water runs clear, as the manual directs. Manufacturers differ: Whirlpool describes restoring the cold-water supply after draining and flushing until the water clears; GE describes briefly applying cold supply with the tank empty and drain open, repeating until clear. Do not combine these methods unless your heater’s instructions call for it.
- Close the drain valve and remove the hose as directed by the manual. If sediment blocks drainage, do not force or dismantle the valve; Whirlpool advises getting qualified help if the tank will not drain.
Refill and restart safely
Never relight or operate the heater while its tank is empty. Reopen the cold-water inlet and, if the manual directs, open hot-water taps to purge air. Wait until water flows steadily from a hot tap before restarting. Then follow the unit’s own lighting instructions; do not guess at a control sequence.
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Rheem RTG Series 7.0 GPM Natural Gas Tankless Water Heater Indoor | 160,000 BTUs High Efficiency On Demand, Continuous Hot Water | Non-Condensing
- High Performance Natural Gas Tankless Water Heater delivers endless instant hot water on demand for whole house residential use | 7.0 GPM at 35°F temperature rise provides 160,000 BTU/hr output for 2-3 simultaneous showers | Never run out of hot water again
- Energy Efficient Non-Condensing Gas Tankless Water Heater with 0.82 Uniform Energy Factor (UEF) saves up to 34% on energy costs vs. 50-gallon electric tank heaters | Indoor installation with direct vent system | Ultra-low gas bills with on-demand heating technology
- Ideal Whole House Tankless Gas Water Heater for large families and multi-bathroom homes with 2-3 water points running simultaneously | Perfect replacement for aging tank water heaters | Space-saving wall-mount design frees up valuable floor space
- CSA Certified Natural Gas Tankless Water Heater with advanced safety features | Digital LED temperature control panel with precision ±1°F adjustments for consistent hot water temperature | Built-in freeze protection, flame failure protection, and multi-point safety system
- Leak Protection – LeakGuard Leak Detection & Prevention protects your home from water damage that detects any internal leak, both large or small
How often should you flush it?
Use the interval in your heater’s manual rather than treating one schedule as universal. The cited A. O. Smith residential gas manual recommends draining and flushing every six months. GE Appliances recommends once a year. These are manufacturer maintenance recommendations, not measured guarantees of performance.
When to stop and call for help
- The drain valve will not drain because sediment is blocking it.
- The valve leaks or you cannot safely control the discharge.
- You cannot confirm the gas shutoff, refill, air-purging, or relighting procedure for your model.
In these cases, leave the heater off and contact a qualified plumber or water-heater technician rather than forcing the valve or improvising a restart.
Quick Recap
SaleBestseller No. 1
Best Value
ThermoMate CZ422NG, Natural Gas Tankless Water Heater Indoor, Up to 5 GPM
- [Max 5 GPM & 113,000 BTU] – The ThermoMate instant water heater delivers hot water on-demand for two showers at the same time, maintaining a stable 105°F (based on 65°F inlet temperature). No waiting, no cold-water interruptions—perfect for busy homes. Its smart flow sensor and control chip adjust heating 20,000 times per second, ensuring ±1°F temperature consistency.
- [Safety & Reliable] - Certified by CSA, this residential gas water heater features boil-dry, freeze, flame-out, overheat, over temperature, timeout, pipe blockage, high-temperature lock, and excessive air pressure protections for safe and dependable operation. The freeze protection automatically activates at 41°F (5°C).
- [Energy Efficient & Save Money] – Built with an oxygen-free copper heat exchanger for efficient heat transfer and corrosion resistance, this natural gas water heater delivers up to 98% thermal efficiency with a UEF of 0.81. Its energy-efficient design reduces energy waste and can lower annual operating costs by approximately 30% compared with traditional water heaters.
- [Easy to Install & Save Space] – Designed for whole house use, this indoor water heater measures only 21"H × 13"W × 7"D and occupies less than one-third of the space of traditional water heater models. Standard 3/4" NPT water inlet/outlet connections, a 1/2" NPT gas inlet, a 3" OD vent connection, and UL-approved 120V plug make installation simple in most homes.
- [Smart Diagnostic Display] - Easily adjust water temperature (90–140°F) and keep track of flow, fan, and flame status on the 3.5-inch LED display. Advanced error codes allow fast troubleshooting, while the UL-certified 120V/5-foot cord keeps the system powered and monitored at all times.
Rank #4
Natural Gas Tankless Water Heater, 4.74 GPM 18L Indoor,Constant propane water heater,Instant Hot Natural Gas Water Heater with Fahrenheit Digital Display,Multi-Protection
- 【Tankless Water Heater】- Natural Gas Tankless Water Heater with Steady Temperature Control & Multiple Safety Protections (Flame Failure Device, Overheating Protection). Only 3.6PSI water pressure required, outputs 4.74 gallons of hot water per minute, maximum temperature raise up to 75℃. Applicable exclusively to Natural Gas (LNG).
- 【Efficient & Energy Saving】- The 4.74 GPM Instant Natural Gas Water Heater features a maximum power output of 81,888 BTU/hour, providing on-demand hot water for 2-3 points of simultaneous water supply to meet bathroom and kitchen hot water demand. This Natural Gas Water Heater’s heat exchanger and main burner are designed with advanced combustion technology, which effectively decreases gas consumption and reduces burning noise.
- 【Quality Material】- Our Water Heater is Crafted from stainless steel, and this Natural Gas Water Heater exhibits high temperature resistance and corrosion resistance. It also features a built-in oxygen-free copper water tank, which helps reduce heat loss and ensures a prolonged service life. It is equipped with an LED smart digital display, allowing you to effortlessly adjust the temperature between 38℃-75℃ according to your preferences.
- 【Easy Assemble and Use】- This water heater is applied with standard 1/2" NPT water fittings and gas inlet, and comes with a 2.4" horizontal vent pipe for quick installation. Note: For normal operation, this product must be installed with proper ventilation and equipped with a smoke exhaust pipe.
- 【Widely Application】- Compared to tank water heaters, it saves over 50% of available space, and is suitable for both bathroom and kitchen hot water demand. It is great for indoor installation in homes, small cabins and remote apartments, and there is no need to install an expansion tank. Note: In cold weather, if the water heater is not used for a long time, it is necessary to open the pressure relief valve to drain the residual water inside the water heater.
Rank #3
Novieex Natural Gas Tankless Water Heater Up to 4.3 GPM 100,000 BTU, Indoor
- 【Note 】 This is 4.3GPM natural gas model. Gas rated pressure: 8.04" w.c. (2.0 kPa), Gas Inlet & Cold Water Inlet & Hot Water Outlet：NPT 1/2", Power Supply: 110V-120V AC/60Hz, Water Pressure Range: 1.5-116 psi (0.01-0.8MPa)
- 【Reliable Hot Water on Demand】 With 100,000 BTU power, this on demand water heater delivers up to 4.3 GPM instant hot water. You can comfortably run a shower, kitchen faucet, and bathroom sink simultaneously—all without any noticeable temperature drop.
- 【Precise Temperature Control】 Enjoy consistent water temperature with a wide adjustable range from 95°F to 149°F, ±1℉ temperature control . The built-in digital thermostat of the tankless water heater ensures your water stays at the desired setting, delivering comfort and safety for every shower and household task.
- 【High Efficiency, Lower Bills】 Say goodbye to the energy and electricity waste of traditional heaters that reheat water nonstop. By leveraging a selectional burner system, our natural gas hot tankless water heater precisely adjusts the flame for the water temperature. You will see a noticeable drop in your energy bills, making it an efficient and cost-effective choice.
- 【Compact & Space-Saving】Compared bulky traditional tanks. Our on demand water heater is wall-mounted, saving over 50% of space and blends seamlessly into utility rooms, basements, or closets. Its sleek appearance and LED touchscreen interface allow for easy and intuitive operation.
Rank #2
Outdoor Propane Tankless Water Heater - 6L 1.58 GPM Portable Gas Water Heater with Handle & Overheating Protection, Instant Hot Water for RV Cabin Camping Boat Barn
- 【Ultra Slim Design】 6L portable water heater product size 11.8 (L) x 5.3(W) x 17.3 (H) inches, only weight 12lb. The compact design is suitable for carrying on the go. This outdoor water heater comes with foldable handle, easy to hang and store. Package includes 5 feet premium on/off shower head, 5 feet gas regulator, 1 set US-standard garden hose adapter, and 1 installation hardware pack. It only takes you a few minutes to install it.
- 【Endless Instant Hot Water】 Maximum power output 40,000BTU/Hr. Get instant endless hot water easily wherever you are. No need to preheat before using tankless water heater. As soon as you turn on the tap, the water flows with your desired temperature. Also, 1.58 gallons of hot water can be produced per minute at the flow rate of 1.58 GPM. Low water pressure start up, just need 2.5 PSI of water pressure to start.
- 【Water Pressure Requirement】 This unit requires a minimum 2.5 PSI starting pressure to operate properly. If your water pressure falls below this threshold, the water heater may fail to start or deliver fluctuating temperatures (hot & cold) during use. Please check your home water pressure BEFORE purchasing — for low-pressure homes, we recommend installing a booster pump. Ensure compatibility to avoid installation issues and enjoy a stable hot water experience.
- 【6-in-1 Protection 】 This propane water heater with CSA approved regulator, safe as per Canadian and US Standard. Features over-heating protection, low water flow protection, dry combustion protection, anti-freezing protection, high water pressure protection and flame failure device. Superior manufacturing quality ensures reliable and long-lasting performance.
- 【Idea for Off-Grid】The camping water heater runs on a standard 20 lb. liquid propane tank and is equipped with an electronic ignition powered by two D-cell batteries. Can be utilized while camping, in RV, hunting, poolside, washing pets or horses, cleaning a vehicle, or even in a tiny house, greenhouse, or cabin. No more chilly outdoor shower anymore.
Manufacturer instructions
- Whirlpool Water Heaters: Draining and Flushing Your Water Heater
- A. O. Smith residential gas water-heater manual (PDF)
- GE Appliances: Water Heater—Draining and Flushing Maintenance
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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