Puzzling Heater Problem

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DangerBoy

DangerBoy

Well-known member
Oct 4, 2018
167
Calgary/Alberta
I had my '95 Hot Spring Grandee drained over the summer, just gave it a cleaning and filled it up for the fall and winter. After filling, I flipped the 20W breaker on to fire up the circ pump. After circulating for awhile I noticed there was an air bubble in the hose between the circ pump and the heater. I moved the circ pump up and down and got the air pocket to move on. When I was doing that, I saw air bubbles come out the discharge end of the heater so I thought I had successfully purged the heater of air.

When I finally flipped the 30W breaker for the heater, I heard the heater come on and the sound of steam and then a good sized air bubble came out of the discharge end of heater and went on up the line towards the flow sensor. I guess I didn't have it completely purged of air after all. When the bubble hit the flow sensor, the tub shut down like it's supposed to. I flipped both breakers off, let the tub sit with no power to it for a couple minutes to reset everything and then started up normally again. Now everything is working perfectly except the heater. I have the control box open and I measure 240 VAC on the output side of the heater relay and I've done a bunch of other testing so I know the relay is working properly and because the relay is closing to send the heater 240V AC, I know the thermistor is calling for heat and I know the flow control switch is working and registering flow because the relay would not close and the heater would not be getting 240V if either of those things were not true.

So it would seem the heater has failed but when I measure resistance through the hot leads going to the heater I get 11 ohms which is what you'd expect for a healthy, intact heater element. I would think that if the heater element fried because of the air pocket, I would get an open circuit when checking resistance through the element. So from that I'd say the heater element is okay but I know the heater is getting voltage and yet the element is not heating up. I am perplexed. Am I wrong about what I should be reading for resistance through the element when it's good vs when it's fried?

I am using the new 6KW Watkins No-fault double tube low-flow heater made by Hydroquip. It does not have a reset button on it.

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It does sound like it should be working. Resistance across the element sounds in range and yes, you would get no reading if it was blown. And if the relay is sending the 240v to the element, it should be heating, unless it goes through some other safety first. Any chance you have an Amp meter? That's the easy way to tell if it's working. How do you know it's not working? Just be feel?
 
I can tell it's not working by touching the tubes on the heater. If the heater is working they get quite warm. They just stay cold. I believe there is an internal mechanical high temp cutoff switch in those heaters but they reset themselves after power off and some cooling. I've been told by Tech support at Watkins that if they are triggered and haven't reset you read about 140 ohm through the heater; not 11 ohms. This is so perplexing... :unsure:
 
I got in touch with a tech at Hydroquip and asked him some questions. They can't give advice or make recommendations to end-users due to liability concerns but he was able to answer most of my questions. Here's what he said:

Yes, there is an internal high limit that can trip and it’s “self-reset” once temp goes down.

o Power needs to be turned OFF to allow the device to reset

o It may take overnight to allow the device to reset given the cabinetry is open and you may remove the back cover of the heater to help

- If you checked resistance of the element from the end of the cord and you do NOT get an open reading, the High Limit is NOT tripped.

o Getting a reading of 11 Ohms would indicate that the element is still good (normal reading about 9.6 Ohms).

To know that the system is heating, an AMP reading should be taken to confirm it is heating or not; you cannot touch the heater in hope that it will feel hot.

Option #2, wait a few hour to see if there is a temperature change.

I did turn the power off for a length of time to allow everything to reset. The temperature of the water in the system was quite cold so it would not have taken much time for the temp of the internal high limit to drop to where it would reset itself.

I thought for sure that in the past I could feel warmth in the metal tubes in the heater shortly after it was turned on even when the water in the tub was cold but maybe my memory is faulty. 🤔

I don't have one of those loop things to determine the amount of current going out to the heater so I went with Option 2. The heater has been turned on for an hour or so now and it seems that the water temp in the tub has gone up a couple degrees F since I turned it on but I need to give it more time before I'm convinced the heater is working fine. It's a 500 US gallon (1,893 L) tub so it takes a while to heat it up. In several hours I'll know if the heater is really working and has the jam to raise the temperature of that large mass of water all the way to 104F/40C. Keeping my fingers crossed... 🤨🤞
 
It's looking good! Temp has gone up 8°F since I turned it on. It's now at 87°F. The real test will be if it can get beyond about 90°F. I once had a situation where the heater could only get it that far but couldn't raise the temp any higher. In that situation, I found that one side of the heater relay had failed so the heater was only getting 120 VAC. This time I know the relay is good and the tub is getting 240 so it should be all good. I guess I'll know if I'm golden and the tub is full of 104°F water when I wake up in the morning.
 
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