Hot tub element resistance

[Pat75]

A neighbor asked me to look at their hot tub. Initially the pump controls weren't working. They hadn't used the tub in a while.

I replaced 2 switches which were bad and the pump works fine. However the heater is not. The relay pulls in but no hot water. I'm measuring a resistance of 8.4 ohms for the resistance on the 1500 watt element. What is your thought on that measurement?
Thank you

 

[LarryFine]

It depends on the wattage rating, which tells us the resistance, and the actual voltage applied.

I suggest doing voltage tests. Is there voltage between the element terminals when the relay is in?

 

[Pat75]

Opps, yes that would be an important thing to know. (Don't get old)
1500 watts, 120 volts, tested with a Fluke

 

[infinity]

I=P/E
1500/120=12.5 amps

R=E/I
120/12.5=9.6 ohms

 

[LarryFine]

1500w / 120v = 12.5a
120v / 12.5a = 9.6 ohms (hot)

120v / 8.4 ohms (cold)= 14.3a
120v x 14.3a = 1716w

 

[LarryFine]

120 volts, tested with a Fluke

Is that at the heating element terminals?

 

[Pat75]

Yes at element.

 

[hillbilly1]

If you are getting voltage at those terminals, then amp clamp test would be next. If it’s working, you should be getting a reading close to what others have posted.

 

[retirede]

Every tub I’ve seen (other than plug-in) have 240V elements.
The cold resistance should be considerably less than at operating conditions.

 

[Pat75]

Yes, this is a plug in tub. Element energizes once circulation motor is turned off. If Tstat isn't satisfied it energizes a relay which poweres element and a small pump. The small pump supplies water to flow through the housing which holds the Element.

 

[g-and-h_electric]

As the owner of a hot tub ( with a 240V heater) It is going to take a looong time to heat the tub. I would do as others have suggested and volt check, and amp out the heater. If those numbers are correct, all is good, just going to take a while.


Howard

 

[Pat75]

Sounds good. Thank you all!

 

[LarryFine]

Every tub I’ve seen (other than plug-in) have 240V elements.

Some are convertible, and run the same element at 1.5w on 120v or at 6kw on 240v.

 

[LarryFine]

Element energizes once circulation motor is turned off. If Tstat isn't satisfied it energizes a relay which poweres element and a small pump. The small pump supplies water to flow through the housing which holds the Element.

Actually, the small pump is the circulation pump, for heating and filtration.

The larger pump is the jet pump, which turns off the heater when on 120v.

On 240, there is enough power available to heat while the jets are running.

Disclaimer: This is all based on it being a convertible tub.

 

[Jraef]

Every hot tub controller I have worked on has a pair of smallish cartridge fuses for the heater elements, like a Bussman FNM-20, on the PC board. My prediction is that you will find and replace those fuses, then discover that the GFCI trips instantly, because your heater elements are "leaking" from having corroded while in the water so long. I've been down this road several times, it's always the same result.