I've had a two-year long, sporadic project to get an old hot tub working so that it would maintain a setpoint of 104 degrees-- it would not maintain temperature and would shoot up to 109 degrees F after maintaining a setpoint of 104 degrees for a while. I did a ton of research, writing and calling, trying to find someone to fix the damn thing It was ridiculously difficult to get information and help. The rare store that would talk to me would recommend that I replace a $600 controller (plus $400 to install) even though they didn't know if that is the problem. I ended up getting a $45 digital temperature controller from Ebay (also available on Amazon), wiring it up, and putting it on a timer. It works great!
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I have a summer house in WA state. It has an old Sonoma Hot Tub redwood spa. I hired a local spa services person to put in a new skid (heater, pump, filter, and controller all mounted on a semi-removable skid) in 2013. The pump/heater is a HydroQuip HT-500T. Starting in 2014, the temperature would swing from 104 degrees (where I set it) to 109 degrees F without warning and without changes to the temperature dial.
I called and wrote about two dozen spa repair places. The skid is theoretically a good idea -- I can disconnect the PVC pipes and bring the skid in to be repaired. In the real world now, however, no one wants to work on something like this. To me, it's a fairly simple setup -- there's a pump, a filter, a heater, and a controller. To just about all the stores within a 60 mile radius, this is a hot tub that they don't want to work on, and they don't want customers to bring in something like this. They only gave me the option of having a technician come out, at the cost of a $240+ round trip service call, to fix it on-site.
Obviously, stores selling hot tubs now only want to sell all-in-one units, where a technician HAS to repair a hot tub on-site. I was disappointed in all the spa stores in Olympia and the surrounding areas. Even the stores that were highly rated on Yelp had no desire to help. I'd reach a front line salesperson on the phone, and no one from the service department ever called me back.
The only person in the state of Washington that was any help whatsoever was Ron Bell of Hot Tub Essentials. Here's what he wrote, which I post here in case it's of help to anyone else with an older hot tub:
I will start off by suggesting you change out your water ... we do coach our customers to change approx.. every 6 months due to the build up of unused sanitizers etc.
Secondly let me say, that those older mechanical thermostats have always had a notorious behaviour of sensitive temp changes on the dial.
Possibly try these tips:
If you have no control over the temperature of your hot tub, here are a few things to look for:
-Ensure the high speed pump is not running for long periods as the friction of the water will raise the temperature.
- Measure the ambient air temperature of the spa cabinet. If you think the temperature is too high, leave the door open to confirm the problem. If the problem goes away when the door is open, use a timer on your spa pack or increase the ventilation of your spa cabinet. If the ambient air temperature is very low, increase the insulation around the equipment. Be careful not to place the insulation too close to the equipment, as this could be a fire hazard.
- Check the pressure switch and make sure the setting isn't too sensitive.
- Make sure the filters and skimmer baskets are clean and not causing a flow problem.
- Check for loose connections on the heater circuits.
- Check the thermostat. Makes sure the probe is all the way in the thermal well and the capillary is not kinked. If all else fails, replace the thermostat.
It may be time to update to a new digital style of pack system. They are actually quite reasonable price wise, and fairly simple to install.
Depending on the option demands of your spa, a pack such as this may be a perfect fit for you:
Let me know your thoughts. We are here to help out however we can.
I really appreciated Ron's reply and tried his solutions that I was capable of, but he was incredibly difficult to reach after that. I emailed him, and he was always "out of town" or "had just gone home for the weekend." His assistant wrote me once that I should try replacing the thermostat, and that it would be a simple matter of hooking up two electrical connectors. I asked if he could point me to the web link so I could order such a thermostat, and he never bothered replying. Evidently selling small items like a thermostat does not represent enough value to any hot tub place for them to bother replying to anyone. I was also just stunned when I finally reached Ron Bell on the phone one Friday morning. We talked, he did not remember my situation, and asked me to re-send my email. I did so, called him back at 2pm, and his store told me that he had already gone home for the weekend. I was just stunned that someone would ask me for more information and then leave for the weekend without returning my call. This was the kind of customer service I got from just about every person in the hot tub business that I talked to.
I started looking farther afield, and found some folks in the Seattle area that seemed like good possibilities. I spoke to this spa repair person on the phone, and he was helpful, but gave a lot of technical information that was over my head. When I emailed him, offering to hire him for his advice, I never heard back:
The Hot Tub Guy: look him up on Yelp, his name is Scott...
I started researching forums on the web. If you've ever done something like this, you will know that finding answers on the web -- if you are a novice -- can be incredibly difficult and time-consuming. However, I had no choice.
I found wiring and other diagrams for my model of hot tub controller (which turns on the heater and pump) online at a website called Aquaman. I also found the thermostat for my controller:
Thermostat, Mech, 5/16" Probe - 18" Capillary (34-0030)
Hydro-Quip Thermostat, Mech, 5/16" Probe - 18" Capillary
Single pole rated at 25 amps with max temp rating at 107°F. Best results are obtained when the bulb is installed in a dry well or groove tube at or immediately before the heater. This is a safety device! If it is found to be out of calibration, do not attempt to perform a field adjustment! Replace bad thermostat with a new one Capillary Length: 18" Bulb Thickness: 5/16
Hot Tub Essentials had this to say about thermostats (they sold a generic one):
Standard Mechanical Thermostat
This classic design will fit most spas. The temperature probe (sensor) is 3-3/4" long by 1/4" thick and on a 36 inch malleable coil. If you don't require the entire length, simply leave it partially wound up.
The thermostat probe should fit completely inside the thermal well. It is OK to replace with a smaller thermostat probe, but not a larger one. If it protrudes outside the thermal well, it should be insulated.
An easy way to insulate the back of the thermal probe is to cut a slit in a Styrofoam cup. Then fill with spray foam insulation and cover the rear of the hot tub thermostat probe.
I bought the thermostat from Aquaman. It was not a difficult thing to replace. One mistake that I might have made - but did not -- was to take the entire controller and heater apart, thinking that the thermal probe might go into the heater itself. Fortunately, I took out the thermostat unit itself along with the thermal probe before dismantling the entire controller, which would have been a huge mess and mistake. I discovered that the thermal probe went into a cylindrical hole inside the heater (the thermal well!), and was not immersed in water.
After trying the new thermostat, I discovered that the controller still did not maintain the temperature of the hot tub. Also, the controller had a mode where it was supposed to turn on only at certain times. That timer mode did not seem to work now.
I decided to try a digital temperature controller. One forum said that he had bought a digital temperature controller and hooked it up to control the temperature in his hot tub -- exactly my problem. He used this temperature controller:
Docooler® Digital Temperature Controller Thermocouple with Sensor (-58~194°F) 10A 110V
This temperature controller sells for less than $16! It would need some wiring done, but this was a lot better than paying a hot tub service technician $240 just to come out to look at my hot tub for 30 minutes, much less paying someone $1000 for a new controller that may or may not work.
This would have been perfect for my needs, but I knew that my hot tub skid drew more than 10 amps. For some reason, there are many temperature controllers on Amazon (such as Inkbird) but all are only rated to 10 amps. My entire skid was hooked up to a household GFCI outlet. It had tripped the outlet a few times but generally had run well.
I knew nothing about household AC wiring until this project. I did use to know some things, but that was 30 years ago. I started doing research, and I learned that household GFCI outlets are rated to 15 amps. Sure enough, when I got to our house, I looked at the outlet and it was rated to 15 amps.
I therefore bought one of these controllers, rated to 30 amps:
Thermostat Heat Cold Temperature Controller 30A Air condition Spa Pool Hot Tub
(This temperature controller seems to work well, and the Ebay seller sells a lot of these and has high ratings. However, I had to return a duplicate order to them, and they are based in Canada. They made the return as difficult and time-consuming as possible!).
Nevertheless, this controller has worked perfectly so far (after I experimented with the settings for a good two days)! Here are the details:
Dual Mini Temperature Controller Thermostat for Controlling temperature on any Heating or Cooling device in the temp range -22 to 230 F (-30 to 110 C) with High output 30 Amp
It displays and control your true temperature and alarms with a BUZZER (AUDIBLE) in an over heating or lower heating emergency. It has a set point and also alarm set point from -22 to 230 F (0 to 110 degrees C)
We also add one water proof temperature sensor for using in water. The sensor detects changes so quickly, you can see the temperature rise and fall degree by degree (with 0.1 degree resolution).
The Controller has 30 Amp relay output, so you can control your heater or cooler by your controller .
This Temperature Controller helps you to control the temperature (accurately with 0.1 degree) and time (minute) on your cocking machine.
Following you will find some of this controller advantages,
1-it is accurate controller with 0.1 C or 0.1 F resolution controlling
2-It is compact size and easily can install
3-It has built in relay , so it doesn't need additional relay or SSR.
4-it can be easily programmed and wired
5-it equipped with 2 type timer too. For example if you fix your set point between 68 to 70 Fahrenheit and your timer on 15 minutes
First Type timer: when push start switch , the heater will work and when the temp reaches to 68 Fahrenheit then Countdown timer will start and keep temperature between 68 to 70F for 15 minutes (you can change this time by setting) and then the controller will turn off the heater after 15 minute automatically.So you are not worry about turning off the heater.
Second Type timer: when push start switch , the heater will work and Countdown timer will start too for 15 minutes. The temperature controller try to reach 68F and will keep temperature between 68 to 70F and after 15 minute from start the controller will turn off the heater Automatically (you can change this time by setting) .So you are not worry about turning off the floor heater.
6-Configurable between Fahrenheit or Celsius
7-Equipped with buzzer alarm for high or low temperature alarm setting
DO NOT ATTEMPT ANY WIRING OF ANY KIND if you lack the knowledge and understanding required. Otherwise personal injury and/or death as well as property damage or loss could occur. WARNING
To wire up this controller, I bought a 14 gauge extension cord from Lowe's for the input and output. I would have been safer buying a 12 gauge extension cord (rated for 15 amps), but the controller is only on for a few hours a day. The wires do not appear to be hot when the controller has been running. I used 12-gauge stranded wire for the other connections, and Wago connectors to connect all the wires (a great find for me):
Wago 222-413 LEVER-NUTS 3 Conductor Compact Connectors 50 PK
I did not know the below, since it's been so long since I've wired anything up. Here are notes from the web if you are wiring up one of these controllers:
For household AC circuits:
The neutral is the longer, fat prong in an outlet, the narrow prong is hot.
In my extension cord, which thankfully followed industry convention: the black wire is hot; white is neutral, green is ground.
I followed the directions from thermomart, and also consulted this Amazon review for the Docooler temperature controller (thanks, Amazon reviewer!):
From the Amazon reviewer: Your hot wire from the wall should go to port 1 and 3. Neutral from the wall should go to 4 and neutral of the receptacle. Port 2 should go to the hot of the receptacle. ground from the wall should go to ground of the receptacle. Do you have an ohm meter? You can check to make sure that your wires are connected to the proper pins of your receptacle and cable.
See here: http://cdn.instructables.com/FD5/BGJG/GZLW99UC/FD5BGJGGZLW99UC.LARGE.jpg
From another reviewer:
To hook up the unit I split an extension cord and put the temperature controller in the middle, which the following instructions detail: I purchased a http://amzn.com/B0002J1KRQ (just an extension cord, but heavy gauge, 18AWG $5.69 ) and cut it 1/3 of the way down from the female end. The only other parts needed are an extra piece of wire the same gauge as the wire in the extension cord 1.5" long and one wire nut (Norb says use the awesome Wago Japanese wire connectors instead). After cutting the extension cord and I then cut back 1.5 of an inch of the main insulation (on both pieces of the extension cable) exposing the 3 insulated wires per piece of cable. Next I stripped all of the insulators back 1/4 of an inch to exposes the wires (3 per piece of cable and twice on each side of the extra wire). The neutral, white, wires I joined together and mounted into terminal block 4. The male cable's (the one that plugs into the wall) black wire and one end of the extra wire were mounted into terminal block 3. The other end of the extra wire was mounted into terminal block 2. The black wire from the female side of the extension (part the crock or other device plugs into) was mounted into terminal block 1. The green (ground) wires from each side of the cable were connected with a wire nut. The two ends of the thermocouple were mounted into terminals blocks 5 and 6. I looped the ground up over the screw extrusion where the back plate mounts and screwed down the back plate (this holds the ground line up and pins the extension cable up into the back and force the ends of the now pieced back together extension cord out of each end of the temperature controller.
After some hiccups, the digital temperature controller has been working perfectly! The temperature probe is in the same thermal well as the old mechanical temperature sensor, and it gives temperature readings that are spot on. The skid is behind a wall, about 4 feet away from the hot tub, in a basement. Therefore it is in a cool environment. The temperature in the thermal well therefore drops very quickly. It will go from 104.5 degrees to 98.5 degrees in as little as 12 minutes.
I've settled on the following settings for the controller:
setpoint = 105 degrees (the hot tub will be about 104 degrees at this setting)
HC = H for heating (the controller turns ON when temperature is lower than the setpoint minus the differential
d = differential = 10 degrees (controller turns ON when temperature in the thermal well reaches 95 degrees).
PT = 0 (this sets a delay so that the controller only turns on after a time set by PT, to avoid turning a compressor or controller on and off too quickly.
Those are the settings that I've used, after much experimentation. I am using the controller in its most basic settings -- adjusting only the setpoint and the differential temperature. The controller goes off and then on every hour or so, and this is controlled by setting the differential higher or lower.
I turned off the alarms, and I tried, but never figured out, the countdown timer (also, every time I tried to set the countdown timer, the entire unit would reset, quite a hassle). At d=10 degrees, it takes from 30 minutes to an hours for the controller to turn back on after reaching the setpoint of 105 degrees. The hot tub loses about 1 degree per hour, and it heats up at the rate of about 2 degrees per hour.
I could let the controller run all day, and this would keep the hot tub at 104 degrees all day. Rather than do this, I've put the hot tub on a standard mechanical timer. (I have it on an Intermatic 2-prong timer now, but will be ordering this one, that has a 15-amp rating and is 3-pronged):
Century 24 Hour Plug-in Mechanical Timer Grounded
The timer turns on from 7AM to 11AM, heating the tub from 100 degrees (it has dropped to 100 degrees overnight) to 104 degrees. It then turns on again from 6pm to 9pm, heating the tub from about 101 to 102 degrees (which it has dropped to during the day) to 104 degrees. I generally use the tub after 10pm, so this timing schedule works well. Obviously if you prefer using your hot tub at different times of the day, you may want to adjust the timer settings, or keep your tub at a set temperature all day, 24 hours a day. You can do either with this temperature controller.