Tankless water heaters need flushing periodically to remove deposits from the boiler. How often you do this procedure depends on factors such as hot often you use your hot water, the mineral content in your water, and whether you have a whole house water conditioning system.
A safer way to remember is to flush your tankless water heater yearly at the same time of year and tie it to a date. As part of the procedure, you should clean out the heater’s water intake filter which you may need to do more often if you have well water. Some tankless water heaters will display a code like FL to tell you it is time to flush, but it may be better to flush it yearly before the code ever appears.
Remember that the chemicals you use in this procedure get into your drinking water so use vinegar only and be safe. Read your owner’s manual first for more specific directions for your particular brand of tankless water heater.
Follow these easy steps and add years of life to your tankless water heater. PlumbingSupply.com sells a Zoehler scale remover kit for about $290. If you feel uncomfortable attempting this yourself, call a plumber like one of the following, but it may cost a couple hundred dollars to have it done.
Five Star plumbers 864.530.0040; AAA Upstate Plumbing 864.801.9000; KT Plumbing 864.663.6105; Ion Water Heaters 866.886.1475.
Homewerks gas valve
Turn off the electricity and gas (if you have a gas water heater) connections to the tankless water heater. You may damage your water heater if you flush it with the power and gas left turned on. Unplug the water heater if possible and be sure it is off.
Rheem supply valves
Shut off the main water supply valves (the yellow handles in the picture) to the tankless water heater. Then turn the red and blue handles to open so water can flow from two hoses you will connect through the pipes. Consult the instructions provided by the isolation valve manufacturer for specifics in using their valve assemblies. It is probably best to shut off the whole house main water valve in addition, just to be sure. The cold water valve on the right shuts off water coming into the tankless water heater from the water supply line but still allows the water to circulate through the pipe from the hose you will attach to a pump.
Attach two about six foot garden hoses to the tankless water heater, one to the intake and one to the output water connections. You may need to buy these adaptors to be able to connect to your water heater’s water connections or to connect the cold water hose to the output of a circulation pump.
Superior Pump 91250 1/4 hp submersible pump
Pour two to four gallons of virgin food grade white vinegar into a five gallon pail, depending on how long it has been since you flushed your system and how dirty it usually gets. You may have to set the pail on a stable table or stool to raise it up closer to the water heater if your hoses are too short to reach. Connect to the pump the hose whose other end connects into the water heater’s water intake supply and set the pump inside the pail. Put the drain hose from the water heater’s output connection inside the pail. Open the drain valves, plug in the pump and turn it on. You should see something coming out of the outlet hose into your pail.
flush tankless water heater diagram
Allow the vinegar, which mixes in with the water, to circulate for about an hour from the pail up to and through the water heater and back down into the pail. The solution may turn a dark murky color as it cleans out the scale. Turn the pump off and drain the vinegar from the heater. Close the cold water drain valve and open the main cold water supply valve. Let fresh water flush through the unit for about five minutes to remove all the vinegar.
EZ Tankless water heater filter
Turn off the cold water main valve and remove the water filter screen in the heater’s cold water intake. Clean all the sediment out of the screen and reinstall the filter back in the cold water intake line.
EZ Tankless pre-sediment filter
You may want to install a pre-sediment filter like this from EZ Tankless one if your cold water intake filter screen contains a lot of debris.
Home Depot AquaPure scale inhibitor
You may want to install a hot water scale inhibitor filter like this stainless steel
connection one by AquaPure. It protects pipes from corrosion and inhibits scale build-up in the water heater for about nine months.
EcoSmart remote control
Turn off (close) the red and blue handle vales at the water heater water connections. Turn on (open) the yellow handle water shutoff valves and the main whole house water shutoff valve. Open a hot water faucet to purge air from the piles and check for leaks at the tankless water heater valves. When there are no leaks, turn on the gas, electricity and the thermostat for the water heater which may be a remote control thermostat like this one from EcoSmart. Set the desired temperature. Check the entire hot water system by running hot water from each location.