My personal Apollo 13 continues: 1995 Hot Spring Grandee overheating

[DangerBoy]

I've been working on bringing a 1995 Watkins Hot Spring Grandee back to life for the last several weeks. I've worked through a number of problems and had a number of setbacks but I'm getting close to having an operational hot tub. I just filled it a couple of days ago and had a number of problems getting it going. I kept getting the blinking light as soon as I powered it up which was really confusing me because the water in the tub was quite cold and air temp was near freezing and the circulation pump was working. Tech support at Watkins told me the reason was that the high temp cutoff sensor in those tubs also have an undocumented low temp cutoff of 10C (50 F). I left a space heater running in the pump compartment overnight and that seemed to do the trick getting that sensor temp up above the low temp cutoff threshold. The system powered up without the high temp cutoff sensor tripping and finally the tub became fully operational.

After getting past that obstacle I was glad to see that the heater was working and the tub seemed to be working okay. It hadn't quite got up to temp by the time I went to bed on Saturday night so I went out to check its progress first thing Sunday morning. The red indicator light was blinking indicating that the high temp sensor tripped and the thermometer I had floating in the tub was maxed out indicating a temp >130F ! Yikes!!

I'm now waiting for the water to cool down enough so I can see if the tub will not go as hot if I set the temp dial to say 1 vs 5 where I had it set when it overheated. My guess is that it won't matter what number I set it at and it will overheat no matter what. There's no way it should have gone north of 130F with the dial set at 5 if the system was working. I'm thinking it might be the heater relay sticking or possibly the thermostat is faulty. The high level shutoff sensor did its job so I kind of think it's okay unless it's supposed to shut the system off way before 130 F.

Can someone help me troubleshoot this and figure out what's gone wrong with this tub?

Thanks

 

[Jimrahbe]

db,

I believe that you are on the right track... I would connect a voltmeter across the heater connections and then set the heat adjustment to max hot and you should see 220 volts across the heater. Then, before it gets a chance to get hot turn the heat adjustment all the way off and the voltage should drop to zero. This should tell you that the heater relay and the control circuit is working.

Then I would set the heat adjustment to say 2 and monitor the heater voltage and see if it shuts off based upon water temperature.

I would assume a faulty water temperature sensor before a sticking relay. The relay might be stuck shut all the time, but that would show up in the first test.

Thanks,

Jim R.

 

[DangerBoy]

First of all, Happy Thanksgiving to our American friends. We Canadians already had our Thanksgiving in early October.

I did a resistance check on the high temp limit and temperature control sensors/thermistors and compared them to a resistance/temp graph I found on-line for those sensors. They were both out of spec and telling the system that the temperature was too low presumably causing the overheating. I bought new sensors and installed them but the tub has still overheated by a long shot - at least according to the floating thermometer I'm using. I'm going to head up to the store and get another thermometer to make sure this old floating thermometer of mine hasn't gone bad although I'm not sure how far out of spec a simple alcohol thermometer can get. If the new thermometer verifies the tub has still way overheated despite the two thermistors having been replaced then what's next on the list of things to suspect?

If the thermostat control board has failed then I'm really hooped. That board is NLA and is pure unobtainium. If it's just a relay then fixing it should be possible.

TIA

 

[DangerBoy]

I pulled the control panel out and opened it up to have a look. The thermostat control board appeared to be in excellent condition. No visible indications of anything gone wrong with it although I realize that's not definitive proof that all components on the board are working correctly. It just makes it a little more unlikely that it's the cause of the problem.

Then I pulled the heater relay out. This is the relay they used for that function https://www.te.com/usa-en/product-1-1393212-4.html#distributor-inventory.

I measured resistance across the two sets of double terminals at the output end and they both measured 0 ohms. The relay is a normally open (NO) non-latching type which if I understand correctly means it should measure open across those two terminals unless there's some sort of or voltage loss of voltage at the input end from the thermostat control board. If that's correct then that would mean the contacts are fused in the relay and that would explain why the tub is overheating. Have I got that right? I hope so because I ordered a new relay (the last one in stock in town I think) and will pick it up tomorrow.

There are several other relays that look the same inside that panel and when I measured resistance across the two pairs of terminals on the output side of those relays I got open so that further reinforces my belief that the heater relay is shot. Hopefully, the heating system will function correctly once I get that heater relay changed out. If the thermostat control board is gone too then I'm either going to blow the tub up with dynamite or go to a digital temperature contol system like this: https://www.ebay.ca/itm/121092751235

 

[DangerBoy]

The old heater relay was definitely toast. You can hear things rattling around inside it when you give it a shake. I replaced it with a brand new heater relay and you'd THINK I'd have it all fixed now but I still might not be out of the woods yet. I can hear the heater relay clicking on and off "click click" repeatedly about every 5-10 seconds and the tub doesn't seem to be warming up. From the last time it overheated with the old relay it had cooled down 105F early this evening so I went in for a soak. I checked it a while ago and it was down to 102F yet I have the temperature dial right up near the highest setting. We'll see in the morning where it is but right now it seems like the system is now no longer heating because the relay never stays engaged for more than a couple seconds at a time. I've already changed out both thermistors and the heater relay. ASSUMING none of those things are defective, if something else is still bad then it seems like it would have to be either the flow sensor or the thermostat control board. My old 1990 Grandee never had any of these issues. The temperature control system on that was much more "primitive" and there was no computer board at all in the tub. Everything was electromechanical and a LOT more reliable than the system these '95-'96 Grandees have in them. Attached is an electrical schematic for my tub.

Can anyone offer any guesses as to why the heater relay is constantly clicking on-off every few seconds?

I'm just about at the point where I'm ready to abandon the OEM thermostat/heater control system altogether and install a digital PID temperature control system.

 

[DangerBoy]

Well, I got out this morning and checked the tub. 96F. Relay still clicking steadily. Pulled off the connector for the flow sensor and the relay clicking stopped. Checked resistance on the flow sensor with the circ pump operating: wide open. There needs to be continuity through that switch in order for the heater relay to close the contacts and allow current to flow to the heater so that has to be why the heater relay isn't staying engaged when sent a signal to engage from the T-stat board.

I know the circ pump is good. It's only a couple years old and the filter that the circ pump draws from is very clean so in all liklihood poor/slow circulation is not the issue unless there's some clogging in the system I can't see. I doubt that though. I think it's much more likely that something's wrong with the flow sensor. Either it's just old and worn out or perhaps maybe the contacts are scaled up with crud to the point where no current is getting through them. If that's the case, maybe I can clean them up and get the switch working again. If not, I guess I'll have to spend more money that I don't have and buy a new one to replace it. I'll have to pull the switch to see if it can be repaired or has to be replaced. In the meantime, I've jumpered the connector for the flow sensor on the control box to bypass the sensor and the tub now appears to be heating. No more relay clicking.

 

[DangerBoy]

Bypassing the flow sensor by jumping the contacts worked and the tub heated up. It now looks like I finally have temperature control!

I shut the tub down and removed the flow control switch. The switch is very simple in design: There is a loose contact which is basically a flimsy metal strip which gets pushed against and makes contact with a rigid/stationary contact if there's enough water current going past it to push it that far. It doesn't detect pressure; it's designed to only allow current to pass through if a sufficient amount of water is moving through the system just downstream of the circ pump and heater. There was quite a bit of scale at the bottom of the loose contact which might of affected it's ability to make contact with the stationary contact. It's hard to say. I also noticed that at its resting position, the contact end of the loose contact was springing back about 1/2" give or take from the stationary contact. That seemed like a long ways for the circ pump current to have to push the loose contact over to touch the stationary contact. Perhaps the metal strip that makes up the loose contact is a bit fatiqued with age. I modified the sensor by gluing in a small piece of plastic at the base of the loose contact which caused the resting position of the loose contact to only be a few mm (maybe 3/16" of an inch) away from making contact with the stationary contact. That way, the switch will still do its job if the flow past it gets really low or zero but a reasonable amount of water flowing past will make it contact the stationary contact and close the circuit without any problem.

I put the modified and cleaned up flow switch back in place, fired up the tub and checked continuity through it while the circ pump was on. I had good stable continuity through it so I removed my bypass jumper from the flow sensor connector on the control panel and plugged the sensor back in. I believe everything is operational and working correctly now. I will see where my temperature is later tonight. Hopefully, it'll be hovering right around 104F where I want it to be.

 

[kimkats]

I have to giggle at your signature...........you should add in "and put it back together again!"

 

[DangerBoy]

I have to giggle at your signature...........you should add in "and put it back together again!"

That's not always guaranteed.

 

[DangerBoy]

I got in the tub last night and the temp was 102F. I turned the temp dial a little more and instantly felt hot water start coming up through the inlet from the circ pump. The heater had kicked on as it was supposed to. This morning, the tub is sitting right at 104 F/40C which is right where I want it. No more runaway overheating and I have full control over the temperature! It looks as though the mission is over and Apollo 13 has successfully splashed down in the Pacific with all hands in good condition. It appears the tub is now fully functional and operating perfectly!!! After all that I hope I get many years of trouble-free reliable running out of this thing. Now I just need to top it up with a bit more water and start with the chemicals.