Hot Tub Spa Parts | Spa Heaters | Heater Troubleshooting

Heater Troubleshooting:

Heater failure is a very common problem, our simple procedure will help you identify heater failure, as a rule of thumb, if your spa is over 3-4 years old it is often more prudent to purchase the whole heater assembly and keep you old one for spares, as you get the sensors included. If the unit is under 3 years old we recommend element replacement by a competent individual.

Background information:

All electrical resistance heaters work by a current being passed through an element, creating heat.  When the current flow is diverted or interrupted, no heat is created, thus your beloved hot tub stops heating, and the temperature drops.

In the majority of the worlds hot tubs, the heater is typically sited under the main control system, the element coil is housed in a heater assembly housing, this is where the heat produced by the element exchanges to the water, as it flows through the tube.  The assembly may also incorporate a selection of sensors: high limit switch/ thermostat/pressure switch. 

Heater Failure.

No heat can indicate a burned-out or broken heating coil, which results in an open circuit.

Before we strip the old heater unit out, we will assume the heater's connection terminals are in good condition to allow you to check that the element is being properly energized by your hot tub's control system. You do this by placing the probes on the 2 x nuts of the heater housing which in essence is the element and check for 220v-240v.

We will also assume the thermostat/pressure switch/high limit switches are functioning properly.

Failure of the heater element can be caused by dry fire.  This occurs when the heater is operated with little or no water present, or a greatly reduced water flow, which can cause the heating coil and/or outer sheath to actually melt.  The element will often have visible signs of damage when a dry fire occurs.  Although properly functioning high limit switches, pressure/flow switches, and thermostats are designed to help prevent this condition, like all devices, these too can fail in hot tubs. Therefore if this has happened we recommend checking the high limit switches, pressure/flow switches, and thermostats for failure before replacing with a new heater element.

Low heat is more often caused by a reduced water flow rather than an electrical problem with the heater itself.  Check your filter to make sure it is not clogged, and that there are no other obstructions restricting spa water flow, it is best to remove the filter and run the spa to see if you filter is impeding water flow. Check the gate valves are all open, and finally, excessive scale build-up on the heater element, as a result of poor  water balancing or hard water zones, can reduce heating efficiency. 

A heater causing the RCD to trip, even intermittently, more often than not indicates a short circuit caused by water intrusion into the heater element's outer sheath. Water can find its way inside at various other entry points, but the most common cause will be a pit hole in the sheath caused by corrosion.  When the electrical current finds a path from the heating coil to the water, the short will cause the RCD to trip.  If you do see a hole in the sheath, there is no need to proceed with testing-- the element has failed

Testing the Heater Element.

Before you begin ensure you disconnect the power at the main RCD switch, then disconnect both power leads from the heater terminals, and then take measurements with an ohm meter.

Acceptable Resistance Range.

To test hot tub heating elements for integrity, use an ohm meter on its lowest setting.  With the meter's test leads, measure the resistance between the two terminals as shown.  The acceptable resistance range for heaters used in most hot tubs is dependent upon the heaters kilowatt rating – as a rule of thumb anywhere between 12 - 22 ohms,. Our experience tells us to look for about 19 ohms or around that mark for a 2 / 3KW rated heater A reading which is too low indicates a bad element i.e. short circuit.  A very high (or infinite) reading indicates a bad element: open circuit or limited conductivity.

Testing for Shorts.

Now test for a short to ground.  On the meter's highest ohm range setting, measure between one element terminal (the element nut) and the sheath (body) of the element.  You should get an infinite reading on the ohm meter, indicating no continuity to ground.  Any ohms reading indicate a short, and a bad element.

Correct Installation of Replacement Spa Heater Elements.

Never bend, push, or twist the electrical terminal.  This could cause a fracture of the epoxy seal and lead to water intrusion.  Always use two wrenches to tighten or loosen the terminal nut.  Hold one wrench on the terminal hex to keep it from turning, and one on the terminal nut for tightening or loosening. This will prevent twisting of the terminal pin, or fracturing its epoxy potting.

Testing Associated Heater Components

If the heater element checks out OK, the problem may be with the high limit switch/thermostat/pressure switches.  These can be tested by disconnecting both wires to each and checking for continuity. 

If you hot tub's heater element, thermostat, and high limit switch are working correctly, you will need to ring us to discuss on 01746 710475

Heater Aftercare.

•             Avoid air locks.  When refilling make sure all air is purged from the plumbing.  Dead air in the heater assembly tube can cause rapid overheating of the element, “dry fire”.  An easy way to help this is to all put the hose pipe in the filter housing when refilling rather than the hot tub itself. Also after refilling the spa, but before connecting the power, loosen a union enough to let trapped air escape (you'll hear it). Hands tighten when all the air has been purged. Make sure your plumbing system is free of leaks.

•             Keep your hot tub’s water balanced.  This will prevent corrosion of heater parts by water which is too acidic (pH to low) and prevent heater scale build-up caused by pH too high. 

•             Maintain sanitizer in hot tubs.  A slimy brown film on the inside wall of a spa may be evidence of a metal dissolving bacteria that is slowly gnawing away at the heater sheath.  This will not be a problem if spa shock is periodically applied and sanitizer maintained.