A tank water heater needs maintenance once a year: a flush to clear sediment and a look at the anode rod. Rheem recommends flushing every year, or every six months if you have hard water. A tankless heater needs draining and descaling every six months to a year. Check for leaks around either type monthly.
Water heater maintenance schedule#
| Task |
How often |
Who |
| Look for leaks, rust and drips |
Monthly |
You |
| Flush a tank heater |
Yearly; every 6 months with hard water |
You or a plumber |
| Inspect the anode rod (tank) |
At the yearly flush |
Usually a plumber |
| Test the temperature and pressure relief valve |
As your manual says |
You or a plumber |
| Descale a tankless heater |
Every 6 to 12 months |
You or a plumber |
| Service an unvented cylinder (UK) |
Yearly |
A qualified installer only |
The anode and tankless intervals come from Rheem's annual maintenance overview, which pairs the yearly tank flush with an anode inspection and suggests draining and descaling tankless gas heaters every six months to a year.
Why flushing matters#
Minerals in your water settle at the bottom of a tank as sediment. On a gas heater, the burner has to heat through that layer before it reaches the water. Rheem lists the signs that sediment is building up:
- Rumbling or popping noises from the tank
- Rusty or cloudy hot water
- Running out of hot water faster than usual
- Longer waits for the tank to recover
- Energy bills creeping up without more use
If you live in a hard water area, you'll probably see scale on your showerhead and kettle too. That's the same stuff collecting in the bottom of the tank, which is why Rheem halves the interval.
How to flush a tank water heater#
Read your heater's manual before you start, because gas and electric models shut down differently. Rheem's basic sequence is:
- Turn off the electricity or gas supply to the heater, and shut the cold water inlet valve.
- Connect a garden hose to the drain valve at the bottom of the tank and run it to a floor drain or outside.
- Open the pressure relief valve to let air in, then open the drain valve and let the tank empty.
- Close the drain valve, disconnect the hose and close the pressure relief valve.
- Turn on the hot water taps around the house, then open the cold water inlet so the tank refills.
- When water flows steadily from every tap, turn them off. Only then restore the power or gas.
That order in step 6 matters on an electric heater. Switching the power on before the tank is full can burn out the heating elements, which are designed to sit underwater.
The water coming out will be hot. Turning the heater off a few hours before you drain lets it cool, and makes it much less likely you'll scald yourself on the hose or valve. Point the hose somewhere nobody's standing.
If you've never flushed the tank and it's several years old, be cautious. Rheem warns that trying to flush hardened sediment yourself can lead to leaks or further damage. Call a plumber if the drain valve won't open or leaks, or if there's heavy rust around the fittings.
The anode rod#
The anode is a metal rod inside the tank that corrodes so the tank lining doesn't. Once it's mostly eaten away, the tank itself starts to rust. Checking it means unscrewing it from the top of the tank, which usually takes a large socket and some force, so many people leave it to a plumber during the yearly service. A rod worn down to its core wire needs replacing.
The relief valve#
Every tank heater has a temperature and pressure (T&P) relief valve, usually on the top or side with a pipe running down. It opens if the tank gets too hot or the pressure climbs too high. Tank manuals typically include a periodic test of this valve. Follow yours exactly, since the water that comes out is scalding.
Never cap, plug or block the discharge pipe to stop a drip. A dripping relief valve is telling you something's wrong, whether that's the valve, the pressure or the temperature. Get it looked at.
Set the temperature to 120°F#
The CPSC recommends setting water heaters to 120 degrees Fahrenheit. Its figures on scalds are sobering: most adults get third-degree burns from 150°F water in two seconds, 140°F water in six seconds, and 130°F water in thirty seconds. Young children and older adults are hurt most often. A lower setting also saves energy.
To check, run the hot tap nearest the heater and hold a cooking thermometer under it. Adjust the heater's thermostat following the manual. Electric heaters often have two thermostats behind access panels, and the CPSC notes both should be set to the same temperature. Turn off the power before removing the panels.
Tankless heaters#
Tankless heaters don't collect sediment the same way, but scale builds up in the heat exchanger, especially with hard water. Descaling usually means isolating the unit with its service valves and circulating a descaling solution through it with a small pump. Your manual will give the method and the solution to use. If your unit shows a scale warning or error code, don't wait for the scheduled date.
UK hot water cylinders#
In the UK, homes with a hot water cylinder often have an unvented one, which runs at mains pressure. The NHBC's homeowner guide says they should be serviced at least once a year by a competent installer, following the manufacturer's recommendations. It is blunt about the alternative: never try to service or alter an unvented system yourself, because it could cause an explosion.
The NHBC also says that if water is dripping or flowing from an overflow or warning pipe, you should find the cause straight away, since it may mean a valve has failed.
When to call a professional#
Call a plumber for leaks from the tank itself, water pooling under the heater, a relief valve that drips or discharges, rusty water that doesn't clear, or anything involving gas lines and venting. If you smell gas, leave the house and call your gas company from outside.
If you rent, report faults to your landlord, who is usually responsible for servicing.
Keeping it on schedule#
Put a monthly ChoreLists.com reminder on the leak check and a yearly one for the flush and anode check, or every six months if your water is hard. Keep the model number, install date and last service date in your home maintenance checklist. If your heater is in a basement with a sump pump, test that the same day.