Master Temp 400 temperature reading much higher than spa
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Posted

Hello all,

My Master Temp 400, which is about three years old, suddenly starting reading the temperature of the water as much higher than the actual temp of the water in the spa. The temp in the spa is about 65% while the heater is saying 101 or higher, making the heater shut off. It tries to turn on again, but immediately shuts off. In looking at posts here in the forum, it appears that it could be the thermistor or the heater control board, both which appear to be easy DYI fixes. I would like to know before replacing either if I am on the right track. Any help would be appreciated.

Thank you,

Steve

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Richard's picture
Tech, Pentair
You are correct on the
Richard's picture
Tech, Pentair
Posted

You are correct on the possibilities of the issue, if you have a multi-meter, you could ohm out the thermistor by disconnecting the brown wires and putting one lead to each side of the terminals and check for ohms tested @ 200. If you water temperature is 65 you should get a resistance reading around 13.4 ohms if you are reading close to 5.0 k, the sensor will need to be replaced, if you are getting the reading around 13, the board will be the issue.

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I would like to follow up on
Posted

I would like to follow up on your reply as it may pertain to my situation. My spa water temp right now is about 52 degrees. When I turn on the heater (Master Temp 400) and spa with my mobi device, the spa water temp reads about 58 degrees. Once the heater lights, then the spa temp readout on the mobi jumps 10-15 degrees at a time until it's at or above the set spa temp of 100 degrees. Then the heater shuts off. This whole sequence takes about 10 seconds. Would the possible causes be the same as you mentioned for the other gentlemen? Thank you!

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