Plumbing Questions? Ask a Plumbing Expert.
Hi, my name is ***** ***** I am a Master Plumber and tankless expert.
First, do you have the same phenomenon when running water from a sink? This could be an issue with the shower cartridge.
If it is a water heater issue, I would first recommend a full descale of the unit. This should be done annually or at least biennially. Also, you should check the intake and exhaust vents and clean them of any debris. Chances are the descale will fix the problem. If you are unsure how to do a descale, it involves a special kit that you connect to the water ports under the unit. You run a solution through the heat exchanger and until all the scale buildup is removed. The kit is about $160 and the entire process is about an hour. If you do not want to do this yourself, you can hire it out. I recommend that you contact the manufacturer for a tankless specialist in your area. Unfortunately, many companies who "say" they perform a descale, do not actually know how it is properly done.
If neither of these work, you may need to have the burner removed and cleaned. This is done with an air compressor and can take some time. It also requires some technical skills. If you are not handy, you may want to hire a specialist.
Most tankless units have multiple sensors. The three sensors we are talking about are 1. Incoming water pressure, 2. Flow rate and 3. Outgoing water pressure.
The unit takes the incoming water temperature, calculates the BTU amount required based on the flow rate to get you the outgoing water temperature. The system verifies and adjusts the flame as needed to maintain the proper outgoing temperature.
The reason a descale is important is that scale buildup can clog the heat exchanger. Now the flow rate will change rapidly based on the scale buildup. This causes the unit to raise and lower the BTU count in an attempt to keep up with the changing flow rates. Doing a descale, cleared the heat exchanger and allows for a steady continuous flow.
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