Runaway temp in my hot tub

[MarathonMan]

I have a question for everyone to see if this has happened to someone else. A couple of weeks ago to temp in our hot tub started to rise above the temp that we set; which was 99°F. I have noticed that pump #1, which is supposed to switch for 5min every hour to circulate the water, seems to be on a lot longer than that. The temp has been escalating up to 102-104°F. I have also noticed that pump #1 also seems to running with less force when switched on than it has historically at its max speed. I'm not sure if there is a way to reset the system or am I looking at replacing this pump. The pump is on its standard or"st" setting. The only way to get the temp down is to open the cover and turn it off at the gfci breaker. Just looking for some advice before calling for a technician. Thanx for help in advance

 

[ajw22]

I think you have a heater relay stuck closed.

What model hot tub?

How old?

@RDspaguy

 

[RDspaguy]

Sounds like a stuck relay. Disconnect the pump and test voltage on low (black to white) and high (red to white) and verify that low turns off when high is on and vice-versa.
Relays can be replaced by an electronics repair guy, or yourself if you feel you're qualified.

 

[RDspaguy]

I think you have a heater relay stuck closed.

What model hot tub?

How old?

@RDspaguy

The heater relay would rapidly overheat the spa, and cause oh errors on digital systems. It would not effect the pump.
Low speed pump relay causes slow overheating and bogs down the pump on high (since low is also still on) sometimes causing the thermal cutout to trip.

 

[Mdragger88]

To be clear, the display is indicating that the heater is on when the temp is rising?

Not sure of your weather there, but when it’s hot & sunny here my tub will get hotter than the set temp because of the sun on the dark cover & the ambient temp. My heater isn’t running though. To compensate for this & to prevent an overheating condition I lower the tub temp.

 

[RDspaguy]

the display is indicating that the heater is on when the temp is rising?

It would not be if a relay were stuck. Only when the thermostat circuit calls for heat. It's more of a "needs to heat" indicator than an "is heating" indicator.

when it’s hot & sunny here my tub will get hotter than the set temp because of the sun on the dark cover & the ambient temp.

Can be a problem, but would not explain the decreased power on "high" jets or the increased (continuous) running in low.

 

[arvil]

I don't know what the hp of the pump is, and don't know what efficiency typical pumps operate at, but, 320 gallons is about 1.2 million milliliters. A one hp pump would add about 641000 calories energy to the water, into 1.2 million ml would be about 1.5°F per hour. But, the pump doesn't operate 100% efficiency, so it's likely less than 1° per hour. But, the spa loses heat from the water to the environment if the temperature is above ambient, so, the temperature rise would certainly be much less. No, the pump is not heating the water. I agree with the stuck relay, or perhaps the temperature sensor is not working correctly and it thinks it's not hot enough and the board is calling for heat. If you can access the temperature sensor, when the water is certainly above the setpoint, check it with an ohmmeter, if you have one, after removing the wires to it, the reading should be infinity, when the water is cold enough to all for heat, the reading should be near zero.

 

[RDspaguy]

I don't know what the hp of the pump is, and don't know what efficiency typical pumps operate at, but, 320 gallons is about 1.2 million milliliters. A one hp pump would add about 641000 calories energy to the water, into 1.2 million ml would be about 1.5°F per hour. But, the pump doesn't operate 100% efficiency, so it's likely less than 1° per hour. But, the spa loses heat from the water to the environment if the temperature is above ambient, so, the temperature rise would certainly be much less. No, the pump is not heating the water. I agree with the stuck relay, or perhaps the temperature sensor is not working correctly and it thinks it's not hot enough and the board is calling for heat. If you can access the temperature sensor, when the water is certainly above the setpoint, check it with an ohmmeter, if you have one, after removing the wires to it, the reading should be infinity, when the water is cold enough to all for heat, the reading should be near zero.

Sorry, but the pump is heating it up. I've been fixing spas for 26 years and can tell you with 100% certainty that they do.
Also, your info on sensors is wrong as well. You will never read either zero or infinity ohms on a sensor, unless your tester is in the wrong mode.
Your desire to help is admirable, but you should know what you're talking about first or it's not helping.

 

[ajw22]

. If you can access the temperature sensor, when the water is certainly above the setpoint, check it with an ohmmeter, if you have one, after removing the wires to it, the reading should be infinity, when the water is cold enough to all for heat, the reading should be near zero.

I suggest you read how 10K temperature sensors work.

Temperature Sensors - Further Reading

www.troublefreepool.com

 

[arvil]

I stand corrected. My bad! I was thinking something like an ordinary thermostat which closes when it wants heat and opens when it's warm enough.