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Caldera Kauai won't hold temperature

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We have a ten-year-old Caldera Kauai with a heater problem.  It will usually heat up to 104 degrees, sometimes hold that for days.  Then, randomly, it won't heat.  Rebooting via shutting off power will usually get it heating again, sometimes not.  Sometimes, it takes several reboots to get it to kick in.  Now that the temperatures are below freezing, this behavior means we can't leave the place for any length of time without worrying it will freeze.  All suggestions appreciated.

1. Plenty of continuous flow out of heater outlet in the bottom center.

2. Timer for clean cycle works on schedule.

3. Never any error codes displayed.

4. Jets all have excellent flow.

5. New filter.

jack vines

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The heater is either not turning on because it can't or because it isn't being told to.  Since you can get to 104 by apparently random powering on and off cycles, my guess is that the heater itself is OK.  That means either a sensor isn't telling the circuit board to turn on the heat, or the circuit board can't turn on the heat due to a logic or relay problem.

Check the water temperature with an independent thermometer.  How does it compare to the tub's display?  A degree or so variance isn't significant, but if the control panel thinks it's 104 and your thermometer says it's 90, than the temp sensor is probably due for replacement.  It's a good idea to replace the hi limit sensor as well.

If the sensor's appear to be accurate, the next suspect is the pressure switch.

When the tub SHOULD be heating, but isn't,  I would check the element to see if it's getting the proper voltage.  Then, check the pressure switch to see if it's closed.  If it's open when the spa should be heating but isn't heating, I would jumper the wires to see if that turns the heater on.  If it does, you probably need a new pressure switch.

If the sensor's are all good, the element is good and you're still not getting heat, my guess is that the circuit board can't turn on the heating element.  Get out your wallet,  a Watkins circuit board isn't cheap.

Dave

 

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On 1/6/2018 at 8:46 AM, Jersey Hot Tub Repair said:

Hi, Dave, thanks for the suggestions:

The heater is either not turning on because it can't or because it isn't being told to.  Since you can get to 104 by apparently random powering on and off cycles, my guess is that the heater itself is OK.  That means either a sensor isn't telling the circuit board to turn on the heat, or the circuit board can't turn on the heat due to a logic or relay problem.  Agree, the heater is obviously OK, as it heats when it gets told to work.

Check the water temperature with an independent thermometer.  How does it compare to the tub's display?  A degree or so variance isn't significant, but if the control panel thinks it's 104 and your thermometer says it's 90, than the temp sensor is probably due for replacement. Temperature display is accurate.

It's a good idea to replace the hi limit sensor as well.  How does the high limit sensor function?  Does it just temporarily shut off the heater at 105?  Is it possible the temperature is running past 104 and being then the heating system is being totally shut off by the high limit sensor? 

If the sensor's appear to be accurate, the next suspect is the pressure switch.  When the tub SHOULD be heating, but isn't,  I would check the element to see if it's getting the proper voltage.  Then, check the pressure switch to see if it's closed.  If it's open when the spa should be heating but isn't heating, I would jumper the wires to see if that turns the heater on.  If it does, you probably need a new pressure switch.  l'll try jumpering the pressure switch.

If the sensor's are all good, the element is good and you're still not getting heat, my guess is that the circuit board can't turn on the heating element.  Get out your wallet,  a Watkins circuit board isn't cheap.  Could turn out to be the circuit board, but solid state stuff is usually good/not good.  It is to be hoped since rebooting gets heat, the problem is a pressure switch.

Thanks for the suggestions.

Jack Vines.

 

 

 

 

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Hi Jack,

The hi limit sensor shuts off the tub if the temperature gets above 115 - 118.  I've never seen a hi limit sensor work intermittently, it usually works or it doesn't.  However, if the heater relay is not shutting off the heater when the PCB tells it to, the tub would continue to heat until the hi limit sensor trips.  In that case, rebooting the hot tub after it cools enough would resolve the problem, at least until the next time it overheats.  I doubt if the hi limit is your problem, my only point is that Watkins recommends replacing the hi limit and temp sensors together.  I usually don't, although about 20% of the time, when one goes the other isn't far behind.

If the problem is the circuit board, it may be a relay that's not opening or closing properly.  It could be due to a defect in the mechanical mechanism itself, or the PCB may not be sending the proper voltages to open and close the relay.   You can send the circuit board out for evaluation and repair.  I don't recommend it because if one component on the circuit board goes bad, chances are the rest of the board isn't far behind.  I've also had less than reliable results on circuit board repairs.

Dave

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Thanks for the suggestions.  I've been watching the temperature display several times a day.  It seems accurate and it has never shown a temperature above the set point; this indicates the high limit isn't the problem.

Yesterday, just to experiment, I tried the UT1 and sure enough saw 105 for an hour or so; then it stopped heating began to coast downward.  After the football game, when we went in, the temp was down to 101.  Manually pressing the "Set" button got the heater working again and a strong flow of hot water raised the temperature one degree while we were in it.

If a function were completely failed, it would be easy to find.  That everything works part of the time makes it more difficult.

jack vines

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Did you every try jumpering the pressure switch?  I've seen older pressure switches stick open or closed.  If your pressure switch is right at the edge of being properly set, vibrations could be causing it to open.  For example, if your particular spa requires 3.4PSI to close the pressure switch and the switch is set for exactly 3.4PSI, the slightest amount of turbulence or vibration could prevent it from closing.  Reduce the sensitivity of the pressure switch by an eight of a turn and see if that helps.

If you reduce the sensitivity of the pressure switch, make sure that disconnecting the circ pump causes the pressure switch to open and the heater to turn off, otherwise you'll be defeating a major element in your overheat protection which can create massive damage if the heater overheats and starts burning things up.

Dave

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 Reduce the sensitivity of the pressure switch by an eight of a turn and see if that helps.

Aha!  So the pressure switch is adjustable?  Thanks for that valuable info which I've not read anywhere in two weeks of searches and researches.  The 1/8-turn should be in or out to reduce the sensitivity?

jack vines

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Turn the screw, or knob, counter clockwise to reduce the amount of pressure needed to activate the switch.   Here's everything you ever wanted to know about pressure switches:  http://www.hottubworks.com/blog/hot-tub-pressure-switch-adjustments/

Dave

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When it comes and goes makes diagnosis difficult.  We were gone for a week, lowered the setting and it held 80 degrees.  We're back and now it's holding 105 (1UT).

jack vines

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