Hot Tub Heaters

Hot Tub Heater Installation and Repair

As a time saver, you may want to test the last switch in the circuit first and work back to the first when you find a switch with power to it, you know everything prior to that one is working, and it may save you checking several switches unnecessarily. Another time saver is to start with the most accessible switches first, since you may find the problem without "digging" into the cabinet (some high-limit switches and thermostats require face plate removal to test). You will develop your own preference, but I proceed with the switches most accessible (and most often the problem), as follows:

PRESSURE SWITCH FAILURE

RATING: ADVANCED

Most pressure switch failure is due to obstructions in the circulation low water in the pool/hot tub; clogged skimmer basket or main drain; clogged pump strainer basket; or dirty filter. Check all these before you touch the pressure switch.

Sometimes the obstruction is in the water supply to the pressure switch. Remove the wires to the switch and unscrew the switch from this tube. Turn on the pump. Water should flow vigorously from the tube. If it does, look in the hole at the end of the pressure switch to be sure it is clear of obstruction.

If no water is coming out of the tube, remove the heater vent top, front header face plate, and flue collectors to expose the end of the tube in the header. Unscrew the tube and remove it. Blow through the tube to clear obstructions. Turn on the pump. Water should shoot out of the hole in the header if there is no obstruction.

If the problem is not in the water supply, adjusting the pressure switch to be more or less sensitive is done with the screw or knob on the switch. When you adjust either way, turn the screw only a quarter-turn at a time, as these switches are very sensitive. Check the operation after each quarter-turn until the heater operates correctly. The heater should fire and stay lighted when the circulation is running; it should shut down within 3 seconds when the circulation stops. If the switch can no longer be adjusted or is rusted out, replace it.

FUSES AND FUSIBLE LINKS

RATING: ADVANCED

As previously described, some 25-volt heater designs include an in-line fuse, like a car fuse, in a bracket on the positive wire coming out of the transformer. Make a visual inspection or use your meter to test for current at a point after the fuse, to test it. If current is not passing through the link, it must be replaced; but remember, you want to determine why the fuse failed in the first place. Is it simply worn out, or is there abnormal heating in the area? After replacing it and restarting the heater, examine the burner components carefully. Look for the following:

•           Is the venting adequate, or is there an overheating condition?
•           Is there soot or debris on the burner tray, causing overheating somewhere?
•           Is the gas pressure low, causing "lazy flame" (yellow flames that seem to "lick" out of the burner instead of strong, blue flames burning straight up)?

HIGH-LIMIT SWITCHES

RATING: ADVANCED

High-limit switches are slightly different in each make of heater, but the principles are the same. Remove the face plate or other protective cover (usually just one screw), and pull the switches with their retainer bracket from the header area. This operation can be done with the pump on or off. Pull the switches from the bracket, noting how this setup is assembled (pay attention, or it can be a jigsaw puzzle to put back together!). Pull the switch from its socket and replace.

ON/OFF SWITCH AND THERMOSTAT

RATING: ADVANCED

The mechanical version of thermostat switches can be tested for current just as the others can. The electronic versions look more complex, but are actually easier to diagnose because they are connected through a terminal block where all the connections are in one place for easy testing.

To avoid heat-related injuries, manufacturers limit their thermostats to 104°F (maximum temperature recommended for hot tubs by most local codes and health laws). Since the mechanical thermostat has an accuracy rate of 3°, these units are calibrated for 101°F (38°C) maximum to allow for an extra 3° inaccuracy. Of course that means it might be 3° the other way, and you may only get your hot tub to 98°F (37°C) or so. Now add bubbling water and a cool evening breeze, and the water only goes to the low 90s.

Electronic thermostats are calibrated to go no higher than 104°F (40°C), because their accuracy rate is within 1/4 of 1°. Still, on a cool, windy night with the jets and blower going full-bore, the water may not get higher than the high 90s. Be aware that the problem may be in the design, not in the components or heater itself.

Replacing the mechanical thermostat requires removing the draft hood top of the heater to expose the oil-filled bulb and tube which are attached to the thermostat dial. Remove this along with the thermostat, and be sure the replacement is the same model, not one with a shorter tube that may not reach the dry well.

Replacing the electronic type means replacing the unit on the panel in the front of the heater only, unless you also suspect the heat sensor (thermostat). If so, the thermostat is found in the same location as the tube / bulb type in the header.

FIREMAN'S SWITCH

RATING: ADVANCED

A fireman’s switch is simply an on/off switch attached to the time clock that shuts off the heater 20 minutes before the pump. The result is cool down of the heater before the water circulation stops, pro-longing component life. You can troubleshoot this switch by jumping across the electrical wires leading to it at any convenient place. If it is defective, replacement is self-explanatory.

INTERMITTENT IGNITION DEVICE (IID)

RATING: ADVANCED

The IID is actually a sophisticated switching device, not an electronic "brain," as some call it. There are no hidden computer chips in this device. IIDs all have the same terminals, although perhaps not in the same location on the box. The power is supplied to the device by the transformer after passing through the control circuit. The IID sends power to the pilot to spark ignition and simultaneously opens the pilot gas valve by sending power to the appropriate terminal on the combination gas valve.

When the pilot lights, the heat creates a voltage which is detected by the IID and which acts as a signal to send power to the main gas valve on the combination gas valve, opening it to send gas to the burner tray.

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