I have an ISE H-770-10 instant hot water heater on my sink. It's a bit old but it works, except that after a period of just a day or so, when you turn the handle for hot water, it takes a long time for any water to come out. It eventually does, and it's hot. It's not leaking out the bottom, and I'm pretty sure it's not boiling out (it's not that hot, and I don't hear it spewing, ever). What could be wrong? (Or do I just need to buy a new one... )

Hi Frank:

The shutoff or water line to the unit may be clogged or clogging up.

You could shut the shutoff and then disconnect the water line from the unit and then direct the water line into a bucket, turn water on and see how the water flows. If water flow is weak then issue may be at the shutoff. If water flow is strong then the unit itself may be getting clogged and will need to be replaced.

Let me know what you think...

MARK