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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 22031
Experience:  Licensed Master plumber with 40+ yrs. experience.
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Our water heater works most of the time, but once or twice a

Customer Question

Our water heater works most of the time, but once or twice a week the water just runs cold...even a whole tub full. Then the next person showers and the water is hot again
JA: How long has this been going on? And how severe is the problem?
Customer: about a month. its more annoying than anything
JA: Do you plan on doing the work yourself?
Customer: would like to as we live in a rural area and just service call is expensive
JA: Anything else we should know to help you best?
Customer: thats about all I can tell you about the symptoms
Submitted: 9 months ago.
Category: Plumbing
Expert:  Rick replied 9 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of you situation.

What is the brand and model number of your water heater?

Customer: replied 9 months ago.
rinnai tankless 2520
Expert:  Rick replied 9 months ago.

If you aren't getting any error messages when this happens the first thing to do is to clean the filter screen at the cold water inlet connection. It's a cap on the side of the fitting. Turn off the water into the unit, then open a hot water (only) faucet until it stops running then close it and unscrew the cap (the filter screen is attached). Clean the screen off then reinstall the cap and turn the water back on. Have a bucket handy since some water will likely remain in the piping and it may drain out when you remove the cap.

Customer: replied 9 months ago.
how do I know if I am getting error messages or not? I am not in the same part of the house as the water heater right now. just ran a whole tub of cold water (from the hot valve), drained that and now ran a whole tub of hot water. That's the typical problem.
Our water is prefiltered at the point where it enters the house, but I suppose I can check the screen later...I doubt that is the problem.
Expert:  Rick replied 9 months ago.

You have to go to the unit and check the display for an error code when this happens. A dirty filter is THE most common cause of this type of problem if there is no error showing on the display. No sediment filter removes everything

Expert:  Rick replied 9 months ago.

I have been called away. I should be back in less than an hour. I'll respond when I get back if you have more questions.

Customer: replied 9 months ago.
I will clean the screen, but it may be a few days before we know if the intermittent problem is really fixed.
Expert:  Rick replied 9 months ago.

This thread won't go away and I'll answer related follow up questions even after you rate me favorably. If cleaning the screen doesn't help then the next time this happens go to the unit and tell me what's on the display.

Customer: replied 9 months ago.
I went to clean the screen, but it is so corroded that I can't get it loose. How much force do I dare use? Is there something I should put on it to dissolve the white and blueish scale deposit.
Expert:  Rick replied 9 months ago.

You can try white Vinegar. Also, if you're water is that hard do you regularly (once a year 2 tops) do an acid flush of the heat exchanger?

Customer: replied 9 months ago.
We have a water softener that seems to use alot of salt. So supposedly we are putting softened water through it. I flushed it last spring with vinegar. How much force can I use on that screen fitting?
Expert:  Rick replied 9 months ago.

You can use a fair amount of force but if it won't come off with medium sized channel lock pliers and something short of all your strength then it's best to leave it alone until/unless you are prepared to replace it.