Serrano Utilities
Flushing the Tankless Hot Water Heater
The tankless water heater has small tubes that the water goes through in the heater. It's possible for those tubes to become restricted (or even blocked) by calcium deposits in the tubes. To remove that calcium before it can block the tubes, and to improve the heating efficiency of the heater, we need to flush the tankless water heaters about once a year with vinegar. Vinegar is a weak acid which will dissolve the calcium.
The tankless water heater on the west side of the house was installed in the January-February time frame and should be flushed each January or February. The tankless water heater on the east side of the house was installed in September and should be flushed each September.
Here's what you'll need to accomplish the flush:
1. A bucket, such as a Home Depot or Lowes bucket. Make sure the bucket is clean. Any trash in the bucket will be pumped into the heater and could block one or more of the heating tubes.
2. A pump. Our pump is kept in the outdoor shed, the left hand one.
3. A set of washing machine hoses. These are kept in the same place as the pump.
4. A large container of vinegar. This one is about 1.3 gallons.
For anyone else reading this, Rheem makes a flush kit but it's expensive compared to what you can buy on your own. I bought this pump from Amazon. You can see the model number in the following picture.
The first step is to turn the heater off. The control is in the laundry room.
Press the "Power" button and the unit will turn off. The display will be blank when it's off.
Here's a picture of the tankless water heater. The cabinet below the heater houses the plumbing. Note the electrical outlet on the side of the cabinet. You'll use this outlet to power the pump.
Open the cabinet.
What you're interested in are the valves at the top of the cabinet.
Begin by turning both valves off (the handles will be pointing at you).
Then remove the caps on the valve ports. You may have to use a pair of pliers. Water will flow out of the ports - don't worry, it's just the water that was in the heater.
By the way, if you ever lose one of those caps you can buy an equivalent cap from Home Depot. They're used to cap the faucets that supply a washing machine when the washing machine is not in use. Ask at Home Depot and one of the employees will find the cap for you.
Take one of the hoses and screw one end to the top of the pump.
Take the other end of that hose and connect it to the port on the blue (cold water) valve.
Take the other hose and connect one end to the port on the red (hot water) valve.
Put the pump and the end of the red valve hose into the bucket. Make SURE the hose attached to the red valve is in the bucket. If it's not, when you turn the pump on, all of the vinegar will flow outside the bucket and no more will be pumped through the heater.
Pour the vinegar into the bucket.
Plug the pump into the outlet.
Check to make sure the vinegar is being pumped back into the bucket. If not, unplug quickly.
Now, wait about 45 minutes.
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After about 45 minutes, unplug the pump.
Remove the pump and hoses from the bucket.
Use a funnel and pour the vinegar back into the container. Not that you're going to use the vinegar again, but you can dispose of it later. The vinegar will be a bit blue. This is from tiny amounts of corrosion of the copper of the tubes in heater. The copper imparts the blue color. Nothing to worry about.
Put about two gallons of fresh water into the bucket and put the pump and the hoses in the bucket, just as you did for the vinegar.
Plug the pump in and let it run for a few minutes. You don't absolutely have to do this step but if you don't, you'll leave some vinegar in the heater and the water will taste of vinegar for a short while. This flush also flushes out the pump. So if you skipped this step, you'd still need to flush the pump out.
While vinegar is a weak acid, it can cause significant damage if left on metal long enough.
After the water flush, unplug the pump and remove both hoses from the valve ports.
Then replace the plugs on the valve ports.
Turn both valves on. I like to turn the hot water valve on first but it probably doesn't make much difference. Check that the there's no leakage around the caps on the valve ports. If so, tighten them.
Then go into the laundry room and turn the power back on with the heater control. You'll see the display light up.
Now, a few cleanup things:
1. I like to run the hot water in the house immediately to make sure everything is working and to flush the air out of the hot water pipes.
2. Wash the hoses and pump very well. You want to get all the vinegar off of them.
3. Hold the hoses up by one end to drain all the water out of them and then roll them up.
4. Put the pump aside and let it dry out well before putting it back into its box.
5. Later, when everything is dry, put the pump and hoses back into the outdoor storage shed.
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