You may be wondering what a cold water sandwich is, it does sound weird doesn’t it? Some of you will already know and it does make sense when you hear what a cold water sandwich is.
A cold water sandwich is when water temperature fluctuate dramatically for a moment. The water can be nice and hot and then suddenly you get a burst of freezing cold and then it returns to hot again.
This is an unfortunate common occurrence in tankless water heaters, particularly gas ones, and it happens when the hot water turned on and off and then on again in quick succession.
It’s because every time the hot water is requested, the ignition sequence has take up to 10 seconds to begin heating the water and when the hot water is turned off and then on again, the ignition sequence restarts.
A way to avoid this is to ensure you aren’t turning the hot tap on and off frequently, and if you had no choice but to do that, be aware that you may get a shot of cold water. It’s quite a nasty experience when in the shower but otherwise, it shouldn’t pose too much of an issue.