Inaccurate reading on spa topside control

My spa is a 2002 Regency Spas, made by National Equipment Mfg. Corp. The circuitboard system has no mfr. name anywhere. There are both a knob thermostat control on the box at the heater and a topside pushbutton control at tubside. The heater is electric Vulcan style (flow-through 2" stainless tube). Pump is 220v and heater is 110v.
The spa heats normally, but quits short of target because the topside digital thermometer reads 5 degrees warmer than actual water temp. Is there a way to calibrate the digital system to get the reading in sync with the actual water temperature?
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I have a much older NEMCO spa, but the system may be similar. With mine, the system of measuring and displaying the temp is controlled by the electronics inside the power pack and it's not meant to be user adjusted. There are several pots inside the power pack that control parts of the settings. One of them does what you want. I figured it out by experimenting years ago, but don't know which one was which anymore. Plus your power pack is probably different. I couldn't find any info avail that detailed what's in the power pack or how it works.
Are you sure it's really a calibration problem? Is it always off by about 5 deg at all temps?
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On Dec 27, 3:22 pm, snipped-for-privacy@optonline.net wrote:

Why not set to where you are comfortable or 5 up
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I think it depends on which way it's off. If it reads 105, but it's actually 100, then that could be a problem. Spas are typically set to go no higher than somewhere around 105. If you want to get that last 5 deg out of it, you wouldn't be able to. I like mine somewhere around 104.
If it's off the other way, or he can live with whatever the incorrect max turns out to be, then I agree, probably easiest thing to do is live with it.
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On Dec 27, 5:31 pm, snipped-for-privacy@optonline.net wrote:

The differential is always the same, and the reading is off in the bad direction. The controls allow settings only up to 106, which means I can't heat above 101 actual water temp. Nice, but not best. I won't say I can't live with it, but in the wintertime warmer would be a lot better.
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If you decide you can't live with it, there are a few possible solutions:
1 - You can call up the manufacturer or local dealer and see what they say. It's possible they have the info available or can adjust it with a service call.
2 - It's possible changing the temp sensor would fix it, as that could be the part that is off.
3 - You could disconnect the wires to the temp sensor. Then use a VOM to measure it's resistance at a couple of temps and see how it changes. From that you may be able to figure out how to put an addional small resistor in series to trick it out by 5 degrees. This depends on whether the resistance goes up or down with temp, not sure which it does
4 - You could open up the power pack. You'll likely find 2 or 3 potetiometers inside. One of them likely makes the adjustment you want. Carefully keep track of what you're doing and change one a 1/2 turn at a time and see what happens, until you find the right one. That's what I wound up doing on my old NEMCO when I ran into a similar problem. If you do that, keep in mind that you may see the display change even when you're not on the pot that really adjusts what you want. For example, there might be one that fiddles with the linearity over the temp range, or similar that will cause the display to read differently when you screw with it. I think mine had 3 pots.
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On Dec 28, 7:14 am, snipped-for-privacy@optonline.net wrote:

The Mfr. of the tub is apparently no longer in business, and I'm in a rural spot where a service call would be pricey in any event. I thought of replacing the sensor, but couldn't see any way a defect there could give a high reading. But, your third and fourth items look good. The spa's outdoors, so it will have to wait until better weather. I'll let you know the results.
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wrote:

The Mfr. of the tub is apparently no longer in business, and I'm in a rural spot where a service call would be pricey in any event. I thought of replacing the sensor, but couldn't see any way a defect there could give a high reading. But, your third and fourth items look good. The spa's outdoors, so it will have to wait until better weather. I'll let you know the results.
Don't know if this is your issue, but I have a different manufacturer (LA Spas), and it has an Economy setting, that only heats if the temp falls more than 5 degrees below the setting to keep the temp within 5 degrees. I have to change to a different setting to get the actual temperature to match the set temperature. Might you have a similar situation?
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wrote:

My spa's guts are pretty basic, really. I don't have your Economy feature. Just an abberant thermostat.
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wrote:

This company sels just about every part for every tub ever made. They have a catalog online with photos and illustrations that are a big help in identifying what brand componets you have. There are even pictures of circuit boards inside of spa packs.
http://aquaticpartsco.com /
Most, if not all, spa makers build the wooden frame, and cast the tub, but buy everything else from someone else. Sometimes the OEM will put the spa maker's brand name on the part as a special touch, but its just cosmetic.
Once you know who made the various parts of your spa, it will forver be easier and cheaper to obtain parts and information.
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On Dec 28, 7:52 am, snipped-for-privacy@dog.com wrote:

It is a problem not knowing who made the controls. You would think there would be a little tag or something somewhere, but I don't see a thing. I'll peruse Aquaticparts' catalog and maybe I'll see something familiar there.
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