When it comes to spa service calls, one of the most common is a ground-fault circuit interrupter (GFCI) that won’t stop tripping.

And more than perhaps any other spa component, a tripped GFCI can point to a whole host of problems. The GFCI acts like a guard, detecting any electricity that’s escaping into an improper part of the circuit, and interrupting the escape attempt.

Whatever the cause of the escaped electrical current, the only way to find the solution is to work through the circuit, testing each connection until the problem becomes clear.

Here, we walk through a service call in which a damaged heater coil was overloading the circuit and tripping the GFCI — and use this example to demonstrate the general principles of GFCI detective work on a spa.

1 Turn on the spa and note when the GFCI trips. If it only takes a few seconds, there’s likely a break in the circuit, which means that the GFCI is detecting a ground fault.

2 The most common cause of a tripping GFCI is a faulty heater, so disconnect all lead wires to the heater, then try resetting the GFCI. If it doesn’t trip at this point, the problem was isolated to the heater. If the GFCI still trips, reattach the lead wires, then begin disconnecting each individual component one-by-one, and repeat this step.

3 If it’s not possible to isolate the problem in the above way, the next step is to remove the cover. Inspect the interior of the GFCI for signs of corrosion, loose wires or other obvious problems.

4 In this case, the heating element is compromised, which is allowing electricity to come into direct contact with the water. The next step is to disconnect the heater from the GFCI, which removes it from the circuit. Then remove the old heater coil and install a new one, making sure no part of the new coil is in direct contact with the outer metal.

5 Whether the problem turned out to be a heater or some other component, the wrap-up is the same: Reconnect all disconnected wires — remembering to properly ground the GFCI — and open all valves that were closed. Then reset the breaker and start the spa again. If the spa runs without tripping the GFCI, the job is complete.