Hot Tub Heater Troubleshooting

Please remember that water and electricity are a deadly combination and do not mix. Use any of the information contained herein AT YOUR OWN RISK. We will not be held liable for any injuries that may result from the troubleshooting advice or installation of any electrical components in your hot tub spa unit.

 

Background information:

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 your 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.

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 world's 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.

The following are areas of concern we cover which we hope to enlighten you.

How do I test whether my heater/heater element is working?
How do I carry out an element Installation?
What do my sensors do and how do I test them
Heater after-care - steps to follow
Heater Troubleshooting

Testing the Heater Element

This video is for reference only, certain elements may not be relevant to your heater or system, also consult the professionals!

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

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 ohmmeter.

Acceptable Resistance Range:

To test hot tub heating elements for integrity, use an ohmmeter 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 heater's 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 3KW rated heater, around 30 ohms for a 2KW and around 40 for a 1.5KW.

A reading which is too low indicates a bad element i.e. short circuit. A very high (or infinite) reading indicates a bad element: an 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 ohmmeter, indicating no continuity to ground. Any ohms reading indicates a short, and a bad element.

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 your hot tub's heater element, thermostat, and high limit switch are working correctly, you will need to email us on info@poolandspacentre.co.uk to discuss

You could also look at the epoxy mould on the element nuts as indicated below - if this is fractured replace the heater or element as this is allowing water to penetrate and foul the system.

Element Installation & Dry Fire Prevention

When installing the element be gentle but firm, never bend, push, or twist the electrical terminal.

This could cause a fracture of the epoxy seal and lead to water intrusion as shown above.

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.

No heat can indicate a burned-out or broken heating coil, which results in an open circuit. This is what 99% of heater failures are about

Failure of your original heater element could have been caused by a dry fire. So please ensure you check your old element to prevent it from happening again thru the correct installation.

Dry fire 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 them with a new heater element.

This is a good example of what a low flow heater looks like when they dry fire. Outside of the manifold is a discoloured (brown or blue) wire terminal overheated with discolouration & melted epoxy seal. Label shrunk & peeled away.

We could tell this was dry-fired from the external damage but still opened it up to see the element. This is a Tifel-coated element that is clearly charred, & easily determined as damaged by the spa controller. The customer that sent it back for a warranty, claimed they installed it and it just didn't work? it did but just for the 90 seconds, it had no water flowing through it!

More than 95% of returns are dry fired, or damaged and do not qualify for a warranty. Here are some photos of a dry fire scenario.

How do I test the M7 Sensors?

The two M-7 Sensors (typically on Balboa systems) located within the heater housing compare the inlet water temperature with the outlet water temperature (regardless of water flow direction) to determine the presence of water, low flow, temperature limits, and operating temperatures.

The system will automatically select the sensor that is exposed to the lowest temperature as the spa water temp controlling sensor.

The sensors in combination with specific software allow the spa to be controlled without the use of external pressure switches, flow-switches, or temperature sensors.

Testing the Sensor Set - only on Balboa systems

1. Check sensor wires for cracks or damage that may indicate the presence of a rodent.

2. Inspect the connections of both sensors on the circuit board. The plugs must be clean.

3. If the sensors are not totally failing but are showing excessive (2 oF / 1.0 oC or more) difference between the two sensors when not heating (a possible cause of Sn/SnS/SENSOR SYNC, HL/HFL/HTR FLOW LOW, and LF/LOW FLOW messages), do the following:

Note which sensor is reading consistently higher(A vs B or t vs H).

4. Unplug the two sensors from the circuit board and interchange them (i.e, plug the one that was in the A or t jack into the B or H jack and vice versa).

5. Press a panel button if any "stray" faults appeared during the process. (Stray faults are normal when sensors are unplugged and then plugged back in while the system is running.)

6. Within a minute or so*, see if the same or other sensor is now reading consistently higher:

- If the same sensor (A vs B or t vs H) is reading higher after the sensor interchange, the problem is on the circuit board. Replace the circuit board.

- If the opposite sensor is now reading higher, the problem is with the sensor(s). Replace the sensor set.

* If you wait more than 2 minutes after plugging the sensors back in, heating may start (even outside a filter in Economy or Sleep mode) due to a stray Cd/CLd/COLDWATER condition usually detected when sensors are being plugged in while the system is running.

7. If there is a message indicating an open or faulty sensor:

- Unplug the sensor set (but leave the original sensors in the heater) and plug in the test sensor set (you can buy these online and it is a good part to have in stock). Put both sensors into the same cup of warm water (ideally above the set temperature, so the spa won't try to heat during this test, as there is no heater protection during this test) and verify that they read the same temperature(within 1?F/0.5?C).
- If the problem is solved, replace the sensor set. If the problem is not solved, do not replace the sensor set.
- Plugin the original sensor set to verify that there is not a connection problem.
- If the problem continues after following the above steps, then replace the circuit board.

8. If you cannot get readings of the sensors on the topside panel

- You can use an ohmmeter to evaluate the validity of each sensor independently (after unplugging the sensors from the circuit board).
- You will need sharp tips on the meter probes to be able to make contact with the little bit of metal of each of the two sensor wires visible through a window on the connector.
- The following chart shows what typical temperatures certain resistance values translate to:

Heater Aftercare

• Avoid airlocks. When refilling makes 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 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 that is too acidic (pH too low) and prevent heater scale build-up caused by pH too high.
• Maintain sanitiser 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 sanitiser maintained.

Heater Troubleshooting - steps to cover

It is always best to try to identify why your heater has failed prior to replacing it as you may replace it only to have the same failure happen again - typically in 90% of cases it is purely due to element failure but it is always best to spend 10 minutes checking

1. Check elements using the above guidelines
2. Check incoming power for proper potential. Do not continue until power checks correctly.
3. Check spa has not been set to economy or sleep (dependant on the spa) / Economy will only heat whilst the spa is on its filtration cycle. (dependant on the spa) / Sleep will only heat whilst the spa is on its filtration cycle and will only heat to 11 deg below the set temperature. (dependant on spa)
4. If the pump runs, but there is no water flow, and hence no heat, you may have an air-lock in the pump's wet end. Correct this problem by closing the gate valve on the suction (intake) side of the pump (If you have one) and then loosen the front pump union just enough to allow the trapped air to escape from inside. Retighten the union, open the valve, and restart the system. NOTE: On newer spa packs, a no-flow condition will normally cause the flow switch to cut power to the heater, and/or the hi-limit switch to trip, disconnecting power to all components.
5. Turn the temperature up. If the low-speed pump engages, check for power at heater element terminals. If power is good but the unit still does not show increased temperature within two hours, replace the heater element.
6. If power is not correct at the heater element, jump outflow/pressure switch connections and recheck power at the heater. If power is now correct, the flow/pressure switch has failed or is incorrectly adjusted.
7. If the pump does not engage with the temperature turned up, check capacitors. Check the valves for restriction or closure, and filters for clogging or reduced flow.
8. The ozone and the blower are typically directly related to heat and if the non-return valve has failed on the ozone or your blower is tripping this can stop the heater from doing its job - disconnect the blower and ozone from the system (switch the spa off first) and then restart, if the spa now heats then connect the ozone then the blower in turn and whichever stops the spa from heating is the cause of the problem.

Heater Troubleshooting - Low Water Flow

Have a look at these things for possible causes....

Are the gate/ball/slice valves open?
Is the water level correct?
Is the filter cartridge dirty? (remove if in doubt and then restart the system)
Are the jets wide open?
Is the impeller clogged?
Is the system primed?
Are all the union fittings tight?

Total lack of heat - Hot tub runs, but does not heat.

If your pump is running and the touchpad says that it is heating but the heat has not gone up in hours? It takes about 8 to 13 hours for some electric heaters to heat a portable spa from tap water cold to hot, so make sure you have allowed time; start off with your air controls turned off and your hardcover on! Typically you will see a 2-3 degree increase and hour, if it is still not heating after that, or is dropping in temperature with the heat light or indicator still on, then firstly:

Are the 0-rings in place?
Is the Hi-Limit switch tripped? (If so, why?)
Are the heater wires burnt?
Is there proper voltage to the pack?
Are all wires in place?
Is there power to the heater? (Indicator light would be on.)
Is the pack in the proper mode for heater operation?
Does the heater work at high speed?

Heater Troubleshooting - Water Gets Too Hot/excessive heat.

Firstly it is important to realise that during hot weather it is quite common for the spa water to overheat. If this is the case remove the cover and turn the temperature down until the water temperature has dropped sufficiently.

Other than that water that is too hot can be caused by several things:

1. Thermostat sensing bulb not applied: Make sure the sensing bulb is applied to the manifold under the heat tape (older models) or inside a thermowell if provided. If in a thermowell, make sure the bulb is centred in the well.
2. Heater relay contacts may be stuck closed: Replace relay (if available) and determine the cause (could be chattering thermostat, low voltage, bad pressure switch, or pump cavitation).
3. Hi-speed pump may have been run for too long: If water exceeds 122 degrees, check the circuit and hi-limit operation.
4. Hi-limit may be defective (most common): If water exceeds 122 degrees and includes the hi-speed shut down circuit, the hi-limit probably needs to be replaced. If it does not include the new circuit, see if the hi-limit is tripped. If the limit is not tripped, it is out of calibration and must be replaced. NEVER RECALIBRATE A HI LIMIT SWITCH.

Heater Troubleshooting - Heater Union Leak

1. Spa must be full and at a temperature of 30c or higher to assess the extent of the leakage.

2. Isolate the heater/control box area by closing the gate valve coming from the filter housing and entering the face of pump 1 (the filter pump). You will need to clamp the 3/4" water tube which feeds the ozone at one side of the heater (if applicable). You will then need to close the gate valve on the opposite side of the heater.

3. Unscrew the heater union (clockwise) and split the nut in two by unscrewing 2 x Phillips head screws. There will be some excess water in the pipework that will run away.

4. Check if the union sleeve sits flush with the heater and the gasket in place. If not, go to section 8.

5. Check the gasket is not perished or split, if it is then replace it with new. If not, put the original back in.

6. Inspect if the heater union collar thread is undamaged, if it is it will need to be replaced. Re-assemble the collar, line up the union sleeve and tighten the union until hand tight. Apply an extra 1/4 turn with a large set of grips being careful not to chew up the collar.

7. Release the gate valves and the clamped ozone pipe if applicable). Allow the water to pass through and prime accordingly. Check for leakages and test.

8. Try physically moving pipework to sit flush. If you cannot achieve this you will need to re-plumb the section of pipework to correct this.