best hot water heater

How to Fix a Clogged Water Heater

Depending which type of heater you own, this could mean a couple different things.  A plugged tankless water heart is a completely different problem with a completely different solution than a tank type heater requires.  We’ll look at both in turn.

Tank Type

When a tank type heater is “plugged up” we are usually referring to the drain valve which is put there to facilitate the regular maintenance flushing required by the manufacturers of the water heater.  If this flushing operation is not done once or twice a year, it is not uncommon to try to flush the water heater and find that no water will come out of the drain valve.  

This problem is actually caused by the failure to frequently flush the heater as instructed, especially if there are water conditions that require treatment with filters/water softeners etc.   The higher the solids content of the water, the more likely the possibility of a clog at the drain valve will occur if the heater is not flushed regularly.

Of course, once the drain valve becomes clogged, the clog must be removed in order to properly maintain the heater. 

A quick note of caution—read the manufacturer’s safety manual and instructions prior to beginning any work on the heater. 

Severe scalding and property damage can occur.  If you don’t feel comfortable after reviewing all of that material, hire a professional plumber to make the fix.

Here’s how to fix that clogged water heater!


First make sure you have a way to get rid of the water from the tank. 

You will need a floor drain or sump pit close by and a way to direct a heavy flow of water to the drain.

Next, shut off the water heater control valve—you don’t need to be making hot water while this is going on! 

Then, run hot water from as many faucets as you like until the water is no longer running hot from the faucets.  Tubs and laundry faucets are usually the quickest way to get this done. Close the faucets when done.

Once the heater is cooled down, shut off the water to the heater.  If you can’t locate a valve on the cold water line to the heater to do this then you will need to shut off the water to the house at the main feed valve/meter/well. 

If you can shut off the cold water feed to the heater, hook a hose up to the drain valve and to a hose faucet outside or inside the home.

This operation could clog the other valves in the house if you don’t make sure they are off. 

Once hooked up, open the hose faucet and then the drain valve on the heater.  

Take the aerator, if any, off the laundry faucet spout. Then open the hot water side only of the laundry faucet.  If this works you will see water under pressure come out of the laundry faucet spout.  Let it flush for a minute.

If you get no water under pressure at this time, lightly tap on the water heater drain valve.  This may break the clog and get things moving.  Once you have success, turn off everything and disconnect the hose from the hose faucet only.

Move the hose to a drain or pump pit and re-open the cold water feed valve to the water heater. Then open the drain valve on the heater tank again.  Water will now flow through the drain and flush debris out of the water heater, extending its life and making it more efficient.

If this operation is unsuccessful, remove the hose from the open drain valve and try to clean out the valve opening with a wire (like a coat hanger or solid electrical wire).  If successful you will see water start flowing.  Remove the wire, shut off the drain valve and reconnect the hose. 

Now you can flush the heater for 7-10 minutes.  Tapping on the drain valve lightly with a hammer while flushing will help to dislodge and break up debris.

If no success you will need to remove the drain valve and replace it.  This is best done by a professional.

Tankless Heater

Tankless heaters will normally shut down and provide error codes before they are completely plugged. 

Don’t ignore this warning!!  If the heat exchanger clogs, you will most likely have to replace the water heater.

That being said, you should have the heater descaled by a pro if this occurs.  If you have heavy solid content in your water, have this process completed every few years to avoid complete failure.

Yes! Plumbing is here to service all your water heater needs from maintenance and repair to replacement and tankless conversion.  

Regular water heater preventative maintenance is provided free of charge to our Premium Club members every year. Call us now for help with your clogged water heater. Phones are answered 24 hours a day.