What could be causing this electrical/heating problem?

DangerBoy

Well-known member
Oct 4, 2018
54
Calgary/Alberta
I have a 1995 Hot Spring Grandee that has the original Series 1 5.5 KW No-Fault heater in it. I recently replaced the temp sensor and hi-temp limit thermistors and the heater relay. The tub has been running flawlessly for these last few months since I did that work and started it up. Recently, we've had a pretty good cold snap here with overnight temperatures sometimes going down as low as -29C (-20 F) and daytime highs around -25C (-13F). Not exactly artic temperatures but on the cold side for here, especially considering the mild winter we were having until this polar vortex swooped in a couple weeks ago. The tub worked fine through the worst of all that easily maintaining the water temp at 40 C (104 F).

We're still in the cold snap but it has warmed up a bit so overnight temps are now around -17C (0 F) and warming up a few degrees during the day. That should be easier on the heater than the colder temps we just went through, right?

A couple nights ago I got in the tub and it wasn't up to temp. Couldn't feel any heated water coming through the circulation inlet. I got into the engine compartment the next morning and found the 30 Amp GFI breaker had tripped so I reset it and the heater came on line again. The water temp at that point was about 32C (90F). I checked the temp that night and it was about 39-ish C (~102 - 103-ish F). I got in the tub and found there wasn't any hot water coming in through the inlet which means that 30 Amp breaker had tripped again.

Below is the wiring diagram for the tub. It shows the 30 Amp breaker basically just powers the heater. As far as I can tell, there's really only two things that could be causing this problem: the heater or the breaker. I suppose it could be bad/corroded connections on or to the heater as well but let's assume that's not the problem for now.

If it was the heater, why would it all of a sudden be drawing so much more current that it's tripping the breaker when it gets close to the normal operating temperature now when outside temps are 13C/20F warmer than a week ago and the tub worked fine through all of that? How do spa heaters generally fail? They're just a heating element so don't they just generally work or not with no "in-between"?

What about the breaker? I don't know much about them and I'm not sure how old this particular unit is. We got that sub-panel for our first tub in the late 90s and I'm not sure if it was new or used then. Knowing me, it was probably used but I can't be sure of that. If it was new at that time it would have about 15 or 16 years of use on it as I went about 3 or 4 years without a working hot tub so the panel wasn't used. Do circuit breakers get "tired"? Could it be that this old breaker just ain't cuttin' the mustard anymore and is now failing at a lower than rated amperage?

What are people's educated guesses on what the likely cause of the problem is? Has anybody had a similar experience?

1995 Grandee electric (MQ).jpg
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
4,438
Northern NJ
More likely the breaker tripping due to the GFI sensing current leakage. Water getting into something electrical that causes current leakage.

You can replace the GFI breaker with a standard breaker FOR TESTING PUPOSES ONLY. DO NOT USE THE HOT TUB OR TOUCH THE WATER WHILE POWER IS ON. If the standard breaker does not trip then it is the GFI sensor.

GFI can be overly sensitive as it ages and trip prematurely. You may want to try replacing the GFI breaker.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
11,427
Bedford, TX
DB,

The first indication of a spa heater going bad is intermittent GFCI trips... The heater cores short to the water just enough to trip the GFCI..

That said, I would follow Allen's advice, as an new GFCI is much cheaper than a heater...

Thanks,

Jim R.
 

DangerBoy

Well-known member
Oct 4, 2018
54
Calgary/Alberta
Okay, thanks for the input. Here's a little more info after I went out and did a little more troubleshooting.

The 30 Amp breaker is tripping the instant I plug the heater plug into its receptacle on the black box. I am measuring 9.8 - 9.9 ohms through the heater element measuring across the two round prongs on the male J&J plug on the heater cord. Isn't that about the right level of resistance you'd expect to see on a heating element?

I get open circuit if I measure continuity between any of the three prongs on the J&J plug on the heater cord. That at least tells me there's no short in the heater power cord or the heater element. I also get open when I measure continuity between any of the poles on the female half of the J&J plug on the black box. That tells me that I don't have a short in the female part of the J&J plug or just upstream of that in the heater relay.

If I reset the 30 amp GFI with the heater unplugged from the black box the breaker will remain set. I take that to mean there's no short or leak ahead of the heater and heater cord? Is that correct?

The instant I try to insert the heater cord into the black box, the 30 Amp breaker trips.

It seems to me that a few months ago when I tested resistance in the heater element before it was somewhere down around 10 ohms but it may have been 11 or 12. I can't remember exactly. But 10 ohms is not a short so can I deduce from that the heater is likely okay?

One other important observation: When I pulled the heater cord out of the black box I could tell that one of the two hot terminals had gotten hot. There was oxidation and a bit of melted black residue on one of the two round (hot) prongs on the male side. I scraped it clean and cleaned out the female parts of the J&J plug with Deoxit and actually honed out the two female hot terminals with a Dremel to expose fresh deoxidized brass to ensure a clean, low resistance connection at the plug. That hasn't seemed to help. The 30 Amp GFI is still tripping the instant I plug the heater cord into the black box.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
4,438
Northern NJ
All your measuring will not find a ground fault. A GFI monitors the current between the two legs of the circuit. If they are not the same it trips saying that some current is leaking to ground through another path. It is very sensitive to current leaks.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
11,427
Bedford, TX
db,

What Allen said... /\

I should not have said "short" which indicate zero ohms... I should have said a small amount of leakage current... as Allen points out, you are not going to see it using a normal Ohm meter.

You can prove it by just doing what Allen suggested in post # 2.. Stick in a non-GFCI circuit breaker (for test only), if the heater works, then the problem is with leakage current in the heater.. The whole purpose of the GFCI is to open the circuit when leakage current is detected.. Sounds to me like it is doing its job...

If this were my hot tub, I would be ordering a new heater...

Sorry,

Jim R.
 
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DangerBoy

Well-known member
Oct 4, 2018
54
Calgary/Alberta
Okay, so I bought a non-GFI 30 amp breaker and installed it. The heater is now working which is a relief as the high today was around -17 (0F) or maybe just a bit higher and it'll drop a few degrees overnight. I'll sleep better knowing the heater is working in the hot tub.

So either the GFI sensor has gotten overly sensitive or the heater is starting to go and there's enough current leakage from the heater to make the GFI trip. How do I know what's actually the problem? A new heater is real expensive but a GFI breaker is pretty expensive too. Home Depot here sells them for $250 CAD. I can get one on Amazon for maybe $190 CAD.

Is there any way to get the GFI breaker tested to see if the GFI sensor is overly sensitive?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
4,438
Northern NJ
You have any other 20A GFI breakers in your house that you can swap in?

I would bet that it’s the heater.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
11,427
Bedford, TX
db,

I have never seen a bad GFCI breaker.. I have seen a couple of bad GFCI outlets that were outside and not covered as well as they should be..

I too would bet on the heater...

Jim R.
 

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