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How often does a tankless water heater need to be descaled?

I have a Rinnai RL94 Tankless hot water heater. It’s not clear to me from the owner’s manual whether the unit needs to be descaled regularly, or whether it’s all right to wait for one of the corresponding “LC” warning codes to appear. I know this depends on the hardness of my local water supply. Is this something that I would be doing pre-emptively, or is it all right to just wait for the warning?

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Hi @jbclements ,

I don’t know the answer but I suppose that you can pre-empt the problem from occurring by occasionally flushing the system as described on p.15 of the manual, to help prolong the life of the heat exchanger.

Perhaps you could check with your local water supply authority as to the hardness of the water in your area to give you some idea of how often this may be required.

Maybe check how quickly the scale builds up in a kitchen electric kettle, just to have some idea of the water quality.

Also on p.14 of the manual it describes how to view the fault history so that you can check if an 00 code is there or not.

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Universal Descaling Method.

Hi, for Descaling any tank less water heater you need these tools,

1. spanner 🔧,

2. Soft water pipes (2 pieces) 3 feet each.

3. Soft disposable Gloves.

4. Small amount of Drain Opener Liquid, we use to clean commode and Sinks. (i.e Harpic, Sweep)

----First of all you have to Close water supply valve to the water heater, and unscrew W.Heater main inlet and outlet Screw,

-----then attach 1 external soft water pipe to outlet connector and 2nd to inlet connector of w.heater.

---Now Put some drain liquid in inlet attached soft pipe,

----for pushing water flow towards w.heater, attaching to any tap and slow release water to pass through the heater, it will clear scale you can repeat 3 or 4 time for best results.

Don't forget to keep outlet pipe in a plastic bag or bin. For safety purposes.

After that leave clean water to pass through heater to remove drain liquid.

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1 Comment:

The question here was not *how* to descale, but *when* to descale.

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John Clements will be eternally grateful.
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