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GE Dishwasher GDF540HGD2BB Heater Element does not work


CaseyCasey

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Hi all, my Dishwasher, GE model GDF540HGD2BB has trouble with the heat element, it does not work at all. I've removed the element and I measured 17.1 Ohms between the element contacts (I assume that means it's still good).  Next in the circuit is what I believe is the thermal safety cutoff sensor. It has the smallest of a red reset button that only travels about 1/16 of an inch. I measured 0.4 Ohms between that sensor (I assume that works as well).  I sadly did not have a chance to put this in to a test mode and verify if the proper AC or DC voltage is being fed to the heater circuit.  Anyone have anymore tests I should do, or should I just start ordering some parts.

Thanks in advance. Long, long time lurker, first time poster :)

Casey.

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11 hours ago, CaseyCasey said:

I measured 17.1 Ohms between the element contacts (I assume that means it's still good).

Correct.

11 hours ago, CaseyCasey said:

Next in the circuit is what I believe is the thermal safety cutoff sensor. It has the smallest of a red reset button that only travels about 1/16 of an inch. I measured 0.4 Ohms between that sensor (I assume that works as well).

Correct

11 hours ago, CaseyCasey said:

I sadly did not have a chance to put this in to a test mode and verify if the proper AC or DC voltage is being fed to the heater circuit.  Anyone have anymore tests I should do, or should I just start ordering some parts.

Heater runs on AC voltage. Run a test cycle and find where that voltage is disappearing, and you will have the solution. Hope this helps!

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16 hours ago, CaseyCasey said:

 Anyone have anymore tests I should do, or should I just start ordering some parts.

Run the diagnostic tests in the mini-manual that should be stuffed into the left leg and see what's actually wrong.

 

 

 

Edited by Terry Carmen
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8 hours ago, THRAMICH said:

Heater runs on AC voltage. Run a test cycle and find where that voltage is disappearing, and you will have the solution. Hope this helps!

Okay, the dishwasher shows no error codes when it enters test mode. When I select heater test mode, I get no voltage at all from the pins for the heater at the connector on the main board.  Short of bench testing each soldered component of the main board, which is beyond my scope of abilities, it looks like a new main board is in my near future.  I'm pretty sure I also tested for voltage last time I had it apart, but since I wasn't sure of the voltage needed for the heater circuit (doesn't show it on the tech sheet) and I also wasn't sure if there was a safety lockout if the circuit wasn't complete.

Thanks fellas!

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On 1/6/2022 at 6:32 AM, Budget Appliance Repair said:

I would be checking the thermistor/flood sensor specs first before replacing the control board.

This is a common fail part on these that will stop the heater from working......

Part number: WD21X10519

http://www.appliancepartspros.com/ShowPartImage.aspx?forumimg=WD21X10519

If that sensor is defective, would it still come into play when the board is in test mode? The GE tech sheet doesn't give specifics for the flood sensor pin outs. The old board when in heater test mode, there was no voltage at the board connector. However a new board still has zero voltage at the heater connector.  The tech sheet doesn't show the thermistor as part of that circuit, just the TCO. So I either received a bad new board, or I bought a new board that I don't need because there is something else coming into play.

I was hoping that the test mode function would bypass other ancillary sensors, override those and turn on the voltage at the connector. 

I've made repairs on several washing machines, a dryer, and a fridge with more luck than this single dish washer.

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Okay, I spent a bit more time in the tech sheet and traced some wires.  I tested the flood switch assembly.  The float sensor works normally, tested open and closed between having the assembly upside down and right side up.  The built in thermistor circuit started around 2.85 K Ohms, after sitting in a cup of hot water it measured 2.4 K Ohms.  I don't have the specifics, temp vs resistance chart, but since it reacts, I'm assuming it works as intended, and therefore shouldn't block the heater circuit from testing and working.

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@CaseyCasey I've never had to work on one of these GE's with that problem - only have worked on one of this type GE dishwashers ever in my area.

I've seen techs in here some say it won't heat in diagnostic or regular use and heard other say in diagnostic test mode the heater works so they originally didn't think there was a problem with the float/thermistor assembly, (there isn't much/?any info on the techsheets about the float switch/thermistor assembly if you aren't familiar with it causing this problem).

Did some research in the tech forums and here's what I found - I'm pretty sure you have a bad Float Switch/Thermistor assembly.

The reason for the discrepancy above - depending on the way the thermistor fails will determine if it will heat or not in diagnostic mode.

If the thermistor is telling the computer that the unit is already hot it won't even heat in diagnostic mode.

Here's a good discussion in the DIY forum that you can access that explains this problem in detail.

https://appliantology.org/topic/66004-ge-dishwasher-does-not-heat-model-gdt580ssf2ss/

Found a list of Ohms and temps at different points in the tech forums that you can't access, here's that info:

Thermistor (in flood switch) Resistance Temperature

20K 50° F

11K 75° F

5.8K 100° F

3.4K 125° F

2.1K 150° F

1.3K 175

With the Ohms of the thermistor reading 2.85K Ohms and 2.4K Ohms when in the hot water - the computer thinks the water is already at between 130 and 145 degree area.

I think you should order a new float switch/thermistor assembly and install.   Most likely should take care of your problem.

 

 

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@Budget Appliance Repair Thank you so much, I'm kicking myself for not listening to you sooner regarding that part.   I was stubborn because I thought it was "working" but it was way out of spec. I'm also kicking GE in the butt for the way their "test mode" doesn't just isolate each component for the test. However during the last test run, I disconnected the float switch connector and BAM now I have the voltage at the heater connector.

I work with remote pressure sensors that use a rheostat and a machine that reads the varying resistance to calculate  pressure... when those fail, they either read open or sometimes get stuck at one value, but they stop changing values with pressure changes. I guess that's why I gave the old sensor a 'pass' in my mind.

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@CaseyCasey And that is the exact problem that comes into play with the diagnostics and not just on dishwasher, (any appliance that uses thermistors for temp readings).   The computer is only looking for an open or shorted thermistor so it will pass the diagnostic test unless it is so far out of the normal ranges that the thermistor should read.  The computer can't tell there is a problem if the thermistor is within the range that it would normally see since it has no idea what the real temp is.

The really crappy thing is GE doesn't even have the thermistor specs on the techsheet, you have to find a service manual to get that info.

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