Gary Burch Owner/25 Years as plumbing Service Technician
Dan, There are a few reasons for hissing at your water heater.
If you drain the water heater of all the hot water making the tank is completely cold, the heater will drip condensate on the burner plate when the heater fire and cause hissing? Or if there is a restriction of some kind at the water heater supply line it will make a hissing noise as the water travels through it?
Have someone run water when you are standing at the heater when it is at full temperature, does it make the noise? If so it’s not a condensation issue.
If your increased water flow is causing more noise it is likely a restriction issue with the supply lines.
Of course Dan there are other possibilities as well, a qualified service technician would need to complete a safety inspection to be sure of any issue before a repair is completed.
Hope this is helpful Gary Burch
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