I have a descaling cost question. I just got a quote for descaling my 5 yr. old Noritz tankless water heater for $400 (this is in addition to the $250 I just paid for a 'temporary' fix so that we could have hot water until they could come back and descale. It seems like for half the cost of a new unit I should just buy a new unit!! Does anyone have any experience with descaling costs? Thank you!!

Remove the bird's nest in the flue.

The 10, 59, 90 and 99 error codes indicate that a Noritz heater has experienced a combustion abnormality. In most cases, it is the result of an obstruction in the heater's flue. Examine the flue to see if it is blocked by debris and clean if necessary.

How To Resolve The Seven Most Common Noritz Tankless ...

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Nov 16, 2015 - This error code involves a breakdown in communication between two tankless water heaters using the Quick Connect Cord. It can occur when more ...

Troubleshooting Noritz Tankless Water Heaters and Error Codes

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Error code 90 and 99 ... Action: Check for the obstructed venting, improper gas burning (flame shape and color change). Ensure the water heater gets the ...

Error Codes for a Noritz Water Heater - Waterheatertimer.org

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Error Code 20 on a Noritz tankless water heater (model EZ98DV) is typically associated with an issue with the "priority" function, which is a feature that allows the water heater to prioritize certain uses of hot water over others.
When the "priority" light is flashing and error code 20 is displayed, it typically means that there is a problem with the priority function and it needs to be reset.
To fix this issue, you can try the following steps:

1. Turn off the power to the water heater by turning off the circuit breaker or removing the fuse.
2. Wait for about 10 seconds and then turn the power back on.
3. Press and hold the "priority" button for about 5 seconds, until the "priority" light turns off.
4. Turn the water heater back on and check to see if the error code has cleared and the "priority" light is no longer flashing.

If the error code 20 still appears and the priority light is flashing, it's best to consult the manual or a professional technician to diagnose the problem.
It's important to note that the error code 20 can also be caused by other issues such as, faulty thermistor, faulty thermistor harness, faulty PCB, etc. So, it's best to get it checked by a professional.

this is a water temperature problem what controls your water temp is not working

1) Recommend replacing tankless with ordinary tank-type gas water heater.
http://waterheatertimer.org/How-to-install-gas-water-heater.html
http://hometips.me/Mar/Which-is-best-gas-water-heater.pdf

2) Tankless cannot be exposed to more than 11 grains hardness in water or unit will fail within 2-5 years. Water softener is required.
http://hometips.me/Tls/Battelle_Water-softening-research.pdf

3) Descaling tankless water heater each year will not restore functionality, or restore efficiency of tankless, nor restore full efficiency to tank-type gas water heater.

4) Bradford White side-by-side testing research comparing their tankless with their tank-type shows that tankless will save $1-8 per month on energy bill vrs ordianry tank-type ....but conclude that tankless 'fall far short of payback' due to maintenance, repair, installation and replacement costs.
Study compared full cost, and not just monthly energy bill, since All costs are energy.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Copy following links for general descaling resources for Tankless:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html#de-lime

2) Add a comment with what you discover

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

This is probably a 16 error code. This code indicates the outlet water spiked above the set temperature for an extended period. It usually means the heater needs to be descaled or the manifold pressures need to be adjusted.

There are many reasons a tankless heater will stop heating water. The first thing I would look for is a flashing red light on the burner indicator. The flash break down goes as follows

continuous blinking - typically means ignition failure or the unit is overheating; look for visible water inside the unit, have your gas pressure checked, or check the flame rod/igniter for buildup of debris

three blinks - typically indicates 16 error code; typically resolved by performing a descale

4 or 5 blinks - exotic error codes; for these you should definitely contact Noritz tech support

If there is no flashing light, first check your filter for debris. If the filter is clean, your flow sensor is probably stuck. Again I'd recommend contacting Noritz tech support to help you clean the flow sensor.

a 16 error code is typically caused by scale formation. I'd recommend performing a descale on the heater.

Three flashes typically indicates the unit is overheating due to scale. I'd try a descale initially and see if that remedies the problem.

This means the thermal fuse has broken and needs replacement. The thermal fuse is a white cord which wraps around the heat exchanger. It typically breaks if the unit is excessively dirty and sooted. Before the fuse is replaced you should make sure the unit is cleaned with compressed air and descaled.