On-demand hot water heater test question...

[bamboozled]

Good morning all, I've asked some questions about my hot water heater in the past but here I go with some more. Is there a test available to determine if the unit is functioning correctly? Mine does indeed provide hot water but the temp goes up and down. The water pressure/volume also goes up and down which does affect the temp of course BUT sometimes the water volume goes up...and so does the temp to where it is scalding. It is under warranty and we called the shop about it. They sent out two boys and of course they turned the water on, felt warm/hot water and said hey, working, and left. Surely there must be a proper way to test these units other than that. Could the current to the unit somehow be fluctuating (wires not tightly connected?) and causing the unit to function at less than maximum? I showered under a 3000 watt unit for years and this is a 4500 watt unit. The 3000 watt unit seemed to function better and provide hotter water though when the 4500 watt unit gets the hot surge it is indeed hotter. Of course "seemed" is not adequate which is why I would like a proper test done. Any ideas what could be the issue or how I can resolve it, short of buying a new one?

 

Thank you.

[Crossy]

How good is your water pressure? Pressure fluctuations, look at your pump.

 

Check the gauze filter at the inlet to the heater.

 

Fizzing connections could cause fluctuations in supply voltage which would affect the heater, you may notice other effects such is flickering lights, burning smell, fire! It won't hurt to check the connections you can access easily. POWER OFF at the mains and verify dead using your meter or neon screwdriver.

 

Unless you are an a parallel dimension the laws of physics say that increasing the flow rate will always reduce the temperature all other things being equal.

 

It's easy to determine how well the heater is heating if you have a thermometer, a clock and a measuring jug. Get out your high-school physics books.

[bamboozled]

Well no lights flicker and there is no other indication of fluctuating voltage so it's not to the house. But I will check the connections they made to the breaker...with main off. Right! for some reason, I did not think of a simple thing like a thermometer, duh! Yes, I am aware the volume of water will affect the temp but it doesn't always seem to go down with increased water flow. The flow and temp both go up sometimes to a point that I can no longer stand under because it's too hot. That is the temp that I rather thought I would be getting with the unit maxed out at 10. But sadly more often than not I am still shivering while showering, this time of year at least. I'll report back. Thanks for your help.

[RichCor]

As you didn't state the make/model of your on-demand water heater I'll just write in general-isms. 

 

Your unit may have an itinerant failure in the control module responsible for modulating the frequency the fast acting solid state triac (power switching triod) is being switched on/off, or the triac itself may be bad. 

 

Triacs are used as a fast acting power relay to send 0% or 100% power to the heating element. Additional circuitry turns the triac on or off many times per second, thus limiting how much 'on' time the heating element receives to control the output temperature. In less expensive units only a bi-metalic sensor is employed as a extreme temperature cut-off switch, while more expensive units may have additional temperature sensors to control the exact heat desired (that may be malfunctioning in your unit).

 

As already suggested, a instant-read thermometer place in container with the on-demand water heater allowed to over-fill it should allow you to view the ongoing temperature fluctuations.  This should give you a bit more to tell the people at the shop what's happening.

[bamboozled]

It's a Hitachi HES-45V about 6 months old now. I quite appreciate the technical aspects of your answer. I always love to know a little bit about how things work. It's fascinating. Ok, it's shower time and I've got my thermometer ready.

[RichCor]

I wonder if there is a specific dial setting that's causing you trouble? Maybe a defective trim pot?

 

I'd suggest setting the temperature control at half-way then just vary the among of water from extremely-low, very low, low, medium, high (full open) and see what your temp readings are.

 

At extremely-low water flow rate adjustments you should be able to hear/detect the reed switch kicking in to allow power to the heating element. 

 

Also at lower flow rates, with the reed switch kicking it, you may hear the heat exchanger boiling to steam (and water output becoming dangerously hot) ...at at some point the bi-metallic safety sensor should trip and cut power to the heating element ...and when the sensor cools after a bit then it allows power to resume to the heating element.

 

As you increase the water flow rate above very-low at this fixed setting you should only notice the heated water outflow temperature dropping as the inflow increases (it shouldn't be getting hotter). 

 

You can also try testing the dial setting at a fixed water flow rate to see if there is an issue with the trim pot at any given position. 

[bamboozled]

My candy thermometer does not seem up to the task. I re-read your post and saw you mentioned an "instant" thermometer. Indeed, mine is too slow to react to the changing water temp. Interesting, last night I had the hottest shower I've ever had in Thailand with high water pressure and volume. So, though I still have no hard numbers to back up my research there is no doubt that the heater is capable of producing much hotter water than it has been producing if everything is working correctly. I should back-track a bit and mention that there is also a water flow problem. The shower is on the second floor on the other side of the house from where the old leaking pump is located (outside of course). I'm in a rental and the owners do not see fit to address this pump as for them it works just fine...even though leaking and always surrounded by a water stain. So when the pump is on the pressure and volume surges and ebbs...of course causing temp problems. I can test without the pump on though, just using the city water pressure. But your comments about switches kicking on or off depending on the pressure AND the 10 minute very hot water/high pressure shower last night (for some unknown reason the pressure was unusually high) makes me think that perhaps the problem is an overall lack of water volume/pressure causing the machine to not work correctly? I know they will cut off when the volume is super low. My pressure is never THAT low unless I turn it down manually. But...makes me think. I do here various noises from the heater, sort of a wheezing sound I believe when the water pressure decreases. Is this the reed switch you talk of? Ah, more likely the heat exchanger boiling. Can I think of the trim pot as an actual pot...of water? Where would I purchase an instant thermometer? I assume these are digital, yes? Thanks for your help RichCor.

[bamboozled]

Some pics... I've been told on this forum that my pump is under powered for a 2-story house. Plus it is ancient. As for the water heater, mine is the HES-45V

[Pdaz]

Looking at that it's a wonder it works at all...

[RichCor]

1 hour ago, bamboozled said:

I should back-track a bit and mention that there is also a water flow problem.
[...]   So when the pump is on the pressure and volume surges and ebbs...of course causing temp problems.

If the water pump is constantly cycling/surging when a water tap is partially opened this might indicate the water reserve / pressure tank has lost it's air cushion  ...or the pressure switches (governing at what line pressure the pump should turn on/off to refill the pressure tank) have gone out of adjustment.

 

Waterpump [Hitachi WT-P200G]
Started by wehugheog, October 17, 2010

 

When the pump is working properly the delivered water pressure should be smooth, changing only slightly as the pressure tank is emptied and refilled by the pump. Constant surging would indicate it needs to be serviced. 

 

 

1 hour ago, bamboozled said:

But...makes me think. I do here various noises from the heater, sort of a wheezing sound I believe when the water pressure decreases. Is this the reed switch you talk of? Ah, more likely the heat exchanger boiling. Can I think of the trim pot as an actual pot...of water? Where would I purchase an instant thermometer? I assume these are digital, yes?

I probably should have just used the term "temperature adjustment knob", the dial on the front of the unit. It controls how often the heating element is cycled on per second (thereby affecting the water temperature). 

 

 

1 hour ago, bamboozled said:

last night I had the hottest shower I've ever had in Thailand with high water pressure and volume

Does adjusting the temperature knob along its range no longer have an affect on the output temperature? 

 

 

As far as thermometers go, an "instant read" is a fast-responding type, can be analog or digital. It should indicate instant-read on the package. Note: some digital thermometers may not be continuous read, and may lock the display once the average temperature is sensed. 

 

              

 

[bamboozled]

Ok, I'll get a thermometer and also test the temp dial on unit. Thank you. There is no doubt that the pump needs to be serviced. The owner of the house refuses to do it in the sense that I brought it up when her son-in-law jack of all poorly done handiwork was here to install some new PVC pipe and they kind of laughed it away. It's like the fix-it guys for the heater. Warm water comes out therefore heater working. Water comes out of tap therefore pump working.