How to Replace 661566 Dishwasher High Limit Thermostat on Whirlpool, Maytag & KitchenAid — Step-by-Step

Your Whirlpool WDF520PADM starts its wash cycle just fine, but when you open the door after the cycle completes, everything's still soaking wet. The dishes are clean enough, but there's water pooled in the cups and your plastics feel cold to the touch. That's your high limit thermostat failing — it's cutting power to the heating element too early or not allowing it to heat at all.

The 661566 high limit thermostat is a safety device mounted on your dishwasher's heating element assembly. When it fails, you'll notice dishes not drying properly, or in some cases, the dishwasher won't start at all because the control board detects a heating circuit problem. This is a straightforward fix that'll save you a $200+ service call.

What You Need Before Starting

This repair takes about 30-45 minutes and requires basic tools you probably already have:

• 1/4" nut driver or socket wrench
• Flathead screwdriver
• Needle-nose pliers
• Towels (for soaking up residual water)
• Flashlight or work light

Difficulty: Moderate — You'll need to access the bottom of the tub, which means removing the lower dish rack and spray arm.

Time Required: 30-45 minutes

Safety First

Unplug your dishwasher or flip the dedicated breaker at your electrical panel. This part is directly connected to the heating element circuit, and you don't want any surprises while working. If your dishwasher is hardwired, confirm power is off with a non-contact voltage tester. Also, run a quick rinse cycle beforehand if possible, or be prepared for some standing water in the sump area when you remove the spray arm.

Step 1: Access the Heating Element Assembly

Pull out the lower dish rack completely. The spray arm assembly lifts straight up or unscrews counterclockwise depending on your model — WDF520PADM and WDT730PAHZ models typically have a twist-lock design. Once removed, you'll see the filter assembly. Pull that out too. Now you can see the heating element loop and the sump area where the thermostat mounts.

Step 2: Locate and Disconnect the Failed Thermostat

The high limit thermostat is a small disc-shaped component with two wire terminals, usually mounted with a single screw or clip on the heating element bracket. On most Whirlpool, Maytag, and KitchenAid models like the MDB7749AWM2 or WDT720PADM, it's positioned near the right side of the heating element loop. Use your phone's flashlight if needed. Pull the wire connectors straight off the terminals — they're friction-fit and don't require tools. If they're stubborn, wiggle them gently with needle-nose pliers.

Step 3: Remove the Old Thermostat

The thermostat is held in place by either a single 1/4" hex screw or a spring clip. Remove the fastener and the old thermostat will lift right out. Check the mounting surface for any corrosion or mineral buildup — wipe it clean with a damp cloth if needed. The thermostat needs good contact with the metal bracket to sense temperature accurately.

Step 4: Install the New 661566 Thermostat

Position your new 661566 thermostat exactly where the old one sat. The flat metal surface should be flush against the heating element bracket. Secure it with the mounting screw or clip. Don't overtighten — you just need it snug enough to maintain contact. Push the wire connectors onto the terminals until you feel them click into place. Give each wire a gentle tug to confirm they're seated properly.

Step 5: Reassemble and Test

Reinstall the filter assembly and spray arm in reverse order. Make sure the spray arm spins freely before pushing the dish rack back in. Restore power to the dishwasher. Run a heated dry cycle or a normal wash cycle to confirm proper operation. About 15 minutes into the cycle, carefully open the door and touch the bottom of the tub near the heating element — it should be warm to hot. When the cycle completes, dishes should come out hot and mostly dry.

Testing After Installation

The real test is the drying phase. After a full cycle, open the door immediately and check the internal temperature. If you've got an infrared thermometer, the tub bottom should read between 140-160°F during heated dry. Your plastics should be warm, and glassware should be too hot to hold comfortably. If dishes are still wet after a heated cycle, double-check your wire connections — a loose terminal is the most common installation mistake.

Frequently Asked Questions

Will this thermostat work on my Kenmore 665 series dishwasher?

Yes, the 661566 is compatible with Kenmore models 665.13153K701, 665.13213K901, and 665.13593K600 among others. Kenmore dishwashers in the 665 series are typically manufactured by Whirlpool and use the same heating element assemblies. Just verify your model number against the compatibility list before ordering.

What's the difference between the high limit thermostat and the regular thermostat?

The high limit thermostat is a safety cutoff that prevents overheating — it opens the circuit if temperature exceeds about 200°F. The regular thermostat (often called the hi-limit or operating thermostat) controls normal heating cycles. They work together. If your dishes aren't drying but the element isn't visibly burned out, it's usually the high limit thermostat that's failed stuck open.

Can a bad thermostat cause the dishwasher not to start at all?

Absolutely. On newer control boards like those in the WDT730PAHZ0 and WDF330PAHS models, the dishwasher runs a diagnostic check at startup. If the heating circuit shows an open (which happens when the high limit thermostat fails), the control board may refuse to start the cycle and blink an error code. Replace the thermostat and the board will clear the fault automatically after a successful cycle.