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Intex Purespa report temperature way too high.

The Base Unit (dated 2019) SB-H10 (the one without the tall stalk) is displaying water temps of 120-140 degrees.

In reality, the water is 65 degrees.

Obviously, the temperature sensor is "broke". But which one is it to replace?

I've had the unit apart, and I've removed three sensors, cleaned them, and put them back in. I've also left it unplugged for about 6 hours.

There are two sensors with hex head, that seem to bolt into the top and bottom of the heater. and there is one on the plastic discharge pipe (this one does not appear to actually go into the water, and is only held in with a retaining arm). Finally, I don't know if it's a sensor, but there is a black wire wrapped like 60 times around the discharge pipe right before it goes back to the spa.

So which sensor is the one I replace?

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Hi @mpking,

What is the model series of the spa?

This is to know if replacement sensors are even available.

Don't know the tub and cannot find a service manual but how many wires are attached to each sensor?

usually sensors are just thermsitors which are resistors whose resistance varies with temperature.

There are two types. NTC negative temp coefficient - as temp goes up resitance value comes down and PTC positive temp coefficient as temp goes up resistance value goes up.

If there is only one wire then the control board is measuring the resistance value of the thermistor with regard to earth. Try removing the sensor and connecting an Ohmmeter between the wire connection terminal on the sensor and a bare metal part on the body of the sensor. Then either cool down the sensor (ice) or warm it up (hair dryer?) and check what happens to the resistance.

If two wires then it's just measuring the resistance value of the thermistor.

Remove the sensor and measure directly across the two terminals with an Ohmmeter whilst either heating or cooling etc.

Usually manufacturers use the same type of thermistor for all applications and not different ones in the one product so the measurements should be very similar.

Just what I'd try.

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@jayeff Intext 28427E 85in PureSpa Inflatable Spa

It's a two wire sensor. I pulled both sensors, and used an ohm meter.

Black plug sensor changed value when I put it in a glass of ice water. 12.52 -19.6 K Ohms

White plug sensor did not meaningfully change. (~1.78 - 1.79 K Ohms)

I assume the white plug is broke

According to the Circuit board, it's the 20-40 C sensor. (The black plug is marked 50C sensor)

white sensor part number (#12580)

https://www.intexdevelopment.com/support...

I did find this repair manual:

https://intexwetset.co.uk/wp-content/upl...

I found this page referencing the sensors

https://www.thermomart.com/Spa-Hot-Tub-P...

Since I like to buy from Amazon, here is the same:

https://amzn.to/2XzaJJG

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@jayeff

Second part of the comment (Too long for Ifixit)

My question. Is there a difference between the sensors? The PCB marks one as 20-40C and another 50C.

Are they actually different?

Or since once is before the heater, and one after, is the 50C one is just a protection device (IE temp over 50C shut the heater off?)

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@mpking

I'm not sure.

maybe try heating the sensor with a hair dryer and check what happens.

I suppose I went the wrong way suggesting ice given that a spa is usually warm and not cold ;-)

Looking at the figures you supplied and the resistance chart supplied in the links the black sensor seemed to indicate a range from 19° to 8°C (66° - 46°F) when placed in ice whereas the white gave a reading of approx. 78°C (170°F) which is wrong even for the ambient temp and it was not in ice water at the time unless you're in an oven.

This is assuming that both sensors are the same thermistor and just packaged in different colours.

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@jayeff I think you have cracked it.

Just before I turned the Spa off, it read 170F.

170F = 78C

For the Black, it read room temp (19C, and then when I put it in ice water, went towards 0C (I pulled it out after about 5 seconds)

So the black is reading nothing special, and the white is so far out of range that it's ridiculous, BUT, matches what the display on the Spa says. So correlation of the bogus value.

I've ordered one of the sensors from Amazon. Here's hoping!

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@jayeff Back for more help.

The part from thermomart is the wrong size. (Thread pattern wrong).

I found this one. It's has nearly identical dimensions. (The only one's that are different won't matter)

https://www.digikey.com/en/products/deta...

But I'm struggling to read the resistance chart. Are they wildly different?

The 25C resistance is the same, but the 40C resistance is 5323.9 on the digikey, and 5829.240 on the thermomart one.

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