On Demand Water Heater

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Thread Starter


Joined Apr 2, 2009
I feel so stupid,I said it looks a reed sensor but never occurred to me to try the it switch with a magnet.

It was a reed sensor. The inlet has a moving part inside. It was not working, so I took it apart and gave a little shock and the thing inside started to rattle.

Now even a little blow switches the heater.

Nothing was broken. Just dirt inside the valve.
Dirty water, Go figure.

Thanks guys.
Another job well done.

But I was hoping to μC it to make it snazzy. But since Sgt could not spice it and me not having a scope, I thought I'll let it go for now.

I did measure the heater voltage though.
At minimum setting I get 115VAC.
So it varies from 115 to 220VAC.

But like to know tht is this an efficient way to control power. This is rather simple method and the mostly used.
I have seen ppl using μC's to control the triac.

What would be the difference from these two methods ?
What effect would this have in the cost, meaning the electricity consumption and the bills


Joined Jul 17, 2007
It seems to me that the method being used is pretty simple and reliable. Just keep the water coming into the heater clean. You should install a filter before the inlet to prevent this problem from recurring, leaving instructions to change the filter regularly.


Joined Jan 28, 2005
I agree with sgtwookie, a filter would be a good idea. Otherwise you are going to find yourself frequently servicing the unit to keep it unclogged.

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Joined Sep 21, 2010
Hi R!f@@, Great to see all fixed, That circuit is probably reasonably efficient, looks simmilar to a AC lamp dimmer, so the heater is actually being pullsed on/off @ has full voltage at max a lower average voltage at lower settings. Daryl
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