Over heating issue

[jse1982]

I recently got a used hot tub and I am having problems with it over heating regardless of what temperature is set. I set the temp to 90 degrees and the tub climbed to 112 degrees and HILI appeared on the display. The Heater icon seems to display correctly at times when it needs to be heating (at or below the set temp). Once it reaches the set temperature, you can hear a relay click and the jets shut down (except for the auxiliary pump that runs 24/7) and the heater icon goes away. Come back a few hours later and the temp has continued to climb. I have to shut the breaker off in order to get the water temp down.
I've done some electrical testing.

Wiring diagram: https://www.dropbox.com/s/07h3g3djujr9yew/IMG_5971.JPG?dl=0
Labeled photo: https://www.dropbox.com/s/rif01l8jytofgln/hottub.JPG?dl=0

On the labeled photo, I marked A-Ground, B-Heater 1, and C-Heater 2. When the water temperature is above the set temperature, I measure VAC with my probes on B and C. I get O volts. I had my wife begin to move the set temperature up above the water temperature and you hear the relay click, jets kick on, and heater icon turn on. The reading jumps to 240V. Seems right to me so far.
Next, with the wires unscrewed from the board at B and C and the set temperature below the water temperature, I placed my probes on A and B and I get a OV reading. Move the set temperature up and cause the relay to click, jets kick on and heater icon turns on. The reading at A and B now reads 120V. Seems right again
Do the same at A and C. I am getting 120V regardless of set temperature above or below the water temperature. Am i right to think that the relay is stuck on and this is where the heater continues to get some power to heat even once the icon and jets are off?

[Vinny]

If the black wires are going to the heater (the photo looks like they are going to the item that's underneath the silver "floor" but I can't tell as there's another black wire coming off of a relay on the bottom. Assuming that the wiring diagram is correct in layout position then yes you have the heater supply/returns. I think the 120 volt is your problem - I would remove that leg and see what happens - please use electrical tape to insulate any open or dangling wires; if the tub stops heating - you have your answer.

[jse1982]

 I did disconnect the wires at B and C (both go to the heater) and the tub did not gain temperature. Well i guess I need to back pedal some now because I took some voltage readings again and regardless of whether the heater should be on or not, I get 120V when I measure across A and B as well as A and C. I previously thought that was only happening across one set. I guess I need some 240V education. Should there be 120V at those locations. My thought is no because I thought there would be no voltage until the relay is on. BUT like I said before measuring across B and C shows that it goes from 0V to 240 when the heater is kicked on and back to 0V when kicks off.

[Vinny]

When I responded my initial thoughts were you need voltage going in and voltage going out but I deleted that part. I don't work on a lot of 220 volt equipment but occasionally I have worked on 440 volt and they always have a positive (black) wire and a neutral (white) wire and I would suspect 220 is similar to that and 120 volt as well.

It may be possible that the relays are stuck open or leaking through or you have something else leaking voltage into that circuit. Just verify (and I'm sure you did) that those 2 points on the board are actually going to the heater although you seem to be in the right place.

Did you check the voltage between ground and neutral?  The 120 volts you are getting now is that with the heater hooked up or with wires dangling? Is there an overtemp switch? It may be the last thing that opens when there is a heating problem stopping the heater from going any further ... Maybe check voltage there as well. OThe problem may be before the relays and it allowing the relay to not fully open but does let it fully close. Is the thermostat mechanical or electronic? If mechanical check that when it truly opens it opens all the way.

Sorry I can't be of more help ... I don't work on these things for a living.

[jse1982]

Well i disconnected both wires leading from the board to the heater element. Let it run for about 5 hours and the thing went from 99 to 105 degrees... How is that even possible? Is it normal for the auxiliary pump to run 24/7? Seems like it should shut off from time to time.

[Vinny]

There are circulation pumps and jet pumps and I guess if the jet pumps are running all the time - yes it's possible. My spa's temp goes up a degree or 2 if I'm in the tub a while and I'm talking about 40 minutes or so. A closed spa, pump running for hours at a time - I can see it happening. It's also possible that the pump is running hot as well.