When we moved into the house, a none functioning hot tub made by Hot Springs Portable Spas sat in the yard. I am not sure about the "portable" part of the name, this thing is not going anywhere, easily. The only information we were given on its condition was that they thought it needed a new heater element. Opening up the access panel I found that the heater element housing was coated with a patch material that looked like plaster. With some help from my father in law, we poked around the electrical controls and concluded that everything was functional. I filled the tub and fired it up. The heater element was getting power and after several hours a noticeable increase in temperature was observed. However the heater element housing repair was not holding and was leaking. Thus the system was shut down and the tub drained so that additional sealant material could be applied to the housing. Once the system became water tight a tub of 102 degree water was produced. I was slightly troubled by this success, since the thermostat control was maxed out. I did not complain too much as I enjoy a beer in the tub after our first snow storm of the season. A weekend of hot tub soaking was all the spa would muster and soon the temperature dropped to 95 degrees.
Upon opening up the panel I was quickly able to identify the various components of the spa. I was greateful that the spa system was pretty simple. The experiance gained from the S2G was very handy.
5-high limit sensor
6-temp control sensor
Cracking the control box I was greeted with a slew of electronic components. Once again it was a relatively simple controller. Rather than have an all inclusive circuit board that does everything, this controller was old school; a bunch of relays, switches, potentiometer, and a few circuit boards made up the brains of the spa system.
6-power out to either circulation pump, heater or jet pump
7-power out to light
8-power out to either circulation pump, heater or jet pump
10-jet on indicator light
My first inclination was to change out the heater element, since that is what the previous owners thought was wrong with the system. However based on some of the "johnny homeowner" repairs I found around the house, I was not so sure that PO thoughts were very reliable. At that time the voice of my old boss popped into my head. He use to say: do not use the "shot gun" approach to repairs. Shoot blindly and hope to hit something. Instead of just replacing parts and hoping that one of them solves the problem, you should figure out what is wrong with the system. I never thought the term "shotgun" approach was very appropriate, instead I think "machine gun" approach paints a more accurate image.
The first thing that I wanted to check was to make sure that the heater element was functioning properly. Messing with the temperature controller yielded clicks from the relay. A relay is a mechanical switch that turns power on and off. Signal voltage from a sensor is very low, and can not power the desired device, thus a relay is needed to handle the power demand of the device when a switched signal indicates it to do so. Tracing the wires back from the heater, I found the particular relay which powers it. This typical relay had six leads, or three pairs. In each pair a lead is for the positive terminal and one for the negative. One pair was for the signal voltage, one for power in and one for power out. I approached the system at a steady state with the thermostat set to max and temp of the tub at 95 degrees. I then took a volt meter and probed the leads. One set of leads showed 120 volts (the spa is a 120 volt system), and the other two showed nothing: the relay was off. Wiggling the temp setting switch around would result in a click. At this time two sets of leads showed 120 and one set show something like 12 volts: the relay was on. Setting the thermostat lower and allowing the system to reach steady state yield a 85 degree spa, turn the controller up would click on the relay. This meant that the heater was turning on and off and that most likely the heater could heat the tub past 95 degrees if the controller told it do so: the heater was good.
When my Spa 2 Go was not able to sustain temperature, the culprit was a failing temperature sensor. So I went to pull the two sensors. However this was a little more involved since I recently epoxied the sensors in place to stop the leaks. So now I had to remove the entire heater housing and bring it into the shop. Once inside I took a Dremel with a small cutter, and with the precision of a dentist went forth cut the the sensor free. With both sensor out I proceeded to test their resistances. Experience from the S2G told me that both sensors of a two sensor system do not fail at the same time and the same rate. The resistance of the sensors were the same at room temperature, a few hundredths of an ohm off, but that is nothing to worry about. Placing the sensors in a bucket of hot water yield an identical drop in resistance. The senors were most likely good. However I eventually found a graph of the sensors that plotted resistance vs. temperature. There was an off chance that the sensors were failing at the identical rate and was causing my problem. But based off the the graph my sensors appeared to be in great shape.
The next logical component that might be the source of my low resulting temperature was the thermostat controller. I however did not have a good test to identify if the current unit was functioning properly or not. All indications pointed that this was the culprit: consistent temperature (I was able to set it to a lower temp and have it stay at the lower temp), wiggling the switch would cause the relay to turn on. Though I was not 100% confident in my diagnosis, base on the process of elimination I was 90% sure. I found a replacement part on-line and speaking with the very helpful tech support, made me feel even better that the part in question was bad. All said and done a new thermostat controller was in the mail and my bank account was $80 leaner. I was taking a risk by not confirming the part was bad, since electronic parts are non refundable, however a house call from a spa repair person would typically incur a $200 bill for the first hour without the cost of parts. A few weeks had also elapsed and the need for the hot tub to be functional was beginning to become dire.
A few days later the part came. I finished epoxying the heater housing and reinstalled all the various components. In a day and a halve's time the tub was filled with 108 degree water.
Bang bang, mission accomplished.
I felt quite a sense of accomplishment and the punch line for old joke about the enigneer and the chalk came to to my mind. One dollar for the chalk, $499 to know where to put the "X".
Now to get the tub up onto my deck.