Troubleshooting high limit switch

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  #1  
Old 07-12-07, 07:19 AM
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Troubleshooting high limit switch

I have a basic Morgan hot tub built in '98. It has been tripping the high limit when it gets close to temperature. I replaced the high limit switch and it actually happens a little bit sooner now. I have tried leaving pump on (non-timer), I have tried running pump on high speed but always the same tripping. I can't get the tub over about 98 degrees and that's with some baby sitting.

The element/thermowells are scale/corrosion free and are perfectly straight.
The high limit capillary is pushed into the thermowell as far as it will go.

I don't believe it is a flow problem, there is good water flow and it even happened with pump on high - normal looking water flow.

I was going to try and and find some kind of capillary thermometer. What is the easiest way to measure water temperature inside an L shaped flow thru?

I am going nuts, my girlfriend is about to dump me if I don't get this thing working.

Thanks for any helpful suggestions,
Joe
 
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  #2  
Old 07-12-07, 07:38 AM
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Oh Joe, girlfriends love those spas don't they....

Most of the time when high limit is tripping and its not water temp related is caused by the heating element. They get a short or something and its an electrical problem. Check home depot or lowes to match up your element, usually you can find one and its alot cheaper then going to a pool store.
 
  #3  
Old 07-12-07, 08:21 PM
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confirmed bad element

looks like a short to ground in the element. I get a few 100k ohms to ground from the terminals, 14.5 ohms across posts. The element is 1.0kW hairpin. I can't find one anywhere, but I found a suitable 1.5 kW element. The flow-thru housing says 1.0 kW max. How can I upgrade to higher current element without buying a complete spa pack? Isn't this a simple switch loop that is limited only by equipment and conductor capacity?
 
  #4  
Old 07-12-07, 08:35 PM
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Though it probably won't hurt anything with the 1.5 you can find the one you need at optimus.com go to spa catalog. You can't buy from them but you can get your part number.
 
  #5  
Old 07-12-07, 08:55 PM
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The hi limit switch has absolutely NOTHING to do with any electrical problems. An electrical short will have NO effect on the hi limit switch. The ONLY thing that will trip (a properly working) hi limit is too high of a temperature.

You might want to check that the element inside the tube hasn't bent or warped and isn't resting right against the dry well that the hi limit probe is in.

If you install a 1.5 kw element into a system designed for a 1kw element you risk frying all the electrical controls. If the system was designed and built around a 1 kw element it may not be capable of properly providing power for a 1.5 kw element. Worst case, a fire starts.
 
  #6  
Old 07-12-07, 09:08 PM
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Thanks for all the valuable information.
So what is effect of non-open from terminal to ground? Isn't that a bad element?

In my first post I described that element and wells are perfectly straight and I have normal water flow. I have tried a replacement high limit switch with same problem.

Regards,
Joe
 
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Old 07-12-07, 09:10 PM
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You're welcome Joe, glad I could help..
Todd
 
  #8  
Old 07-12-07, 09:21 PM
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Could also be a bad, or partially clogged pressure switch . The heater should turn off the instant the pump turns off. Every time the pump turns off. If the heater takes a second or two to turn off, it can cause the water in the heater to overheat and trip the hi limit.
 
  #9  
Old 07-12-07, 09:26 PM
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As I stated in my first post, I have pump on continuous, not timer. still trips high limit. Also, run pump on high speed, still trips high limit.
 
  #10  
Old 07-27-07, 08:43 AM
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still tripping

I have replaced high limit switch, heater element and pressure switch. I was very hopeful tat I would finally be able to use tub tonight. The pump was on continuous (not timer) I got up this morning and the flipping thing was flipped.

There appears to be very good flow. What the heck now?

This is a very simple pneumatic control, doesn't have a timer. I think I will put a thermometer in the thermo well. I do not think it is the thermostat since it trips before getting to temp, but I should I replace that also.

Any ideas?

Thanks people.
 
  #11  
Old 07-27-07, 02:56 PM
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Ok, explain to me what it is doing...

When you turn on system does it imediately throw high limit or does it run and heat?? How long does it run before tripping? What temp does water get to?
 
  #12  
Old 07-27-07, 07:43 PM
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gets up to 99-100 degrees and trips high limit

new high limit switch
new heater element
new pressure switch (even though it trips even when pump is on continuous, U)
new thermostat today

I have put an RF temp probe with remote alarm in jet - 99 degrees. High limit tripped without monitor alarming.

I put probe partially in dry well best I could (pressure switch is in the way for straight probe). GF says alarm went off at 105, she checked and pump still running then went back to 99. 5 minutes later alarm went off at 109, pump was checked and switch was tripped. Monitor jumped up to 119 (a few minutes after tripped) then went back to 99. High limit switch will not reset yet. Monitor has been steadily decreasing now down to 94 (barely stuck in dry well).

I suspect the RF temperature monitor may be getting some interference, but it is suspicious it coincides with tripping switch.

Can a hot running pump cause this?

I am about to buy another high limit switch. Pretty soon I will have enough parts to rebuild another tub.

Thanks for any additional suggestions.
 
  #13  
Old 07-28-07, 08:53 AM
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Problem solved!

I finally decided to see exactly what these components were doing. The new thermostat was cutting off at 100 degrees at the jet. I took the thermostat, the high limit switch, thermometer and a pan and put the sensors in the pan. I filled the pan with hot/cold water to raise/lower the temp and see at what temp they tripped. The thermostat was supposed to be factory set at 107 max. Turns out to be 102-103 and the High Limit trips around the same temperature (supposed to be 121 factory set). I re-calibrated high limit for 115 and re-calibrated max thermostat temp to around 107. I put some finger nail polish on the adjustment screw threads.

I swapped out the two new, re-calibrated components and fired up the tub. I set my RF temp alarm at 105 and when it reached that point I went and turned down the t-stat to maintain that temp.

It's the next morning, tub is still running, water temp is 105!

I took the old components and sink tested them. They were both badly mis-calibrated, the high temp of the old thermostat was higher than the high limit trip.

I now have a spare everything in preparation for spa Y2K.

If I would have pulled and sink tested the original high limit I would have resolved this a long time ago.

Thanks for all the tips.
 
  #14  
Old 07-28-07, 04:08 PM
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Good work, you're hired... GF happy...Will be a good day....
 
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