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May 10th, 2012, 05:34 AM
#1
Circulation pump turns on and of forever....
Brand:
Bosch
Age:
1-5 years
I bought this dishwasher for cheap thinking all it needed was a circulation pump. So far I have replaced the circ pump, the control board, the water fill valve, and the HTC. I am way past thinking I got screwed on this deal but now it's a matter of principle and I'm so deep into it now I can't give up..
I have a copy of the technician's service manual. The symptoms are as follows; When I run the test program and the unit cycles to the water heating stage, the circ pump turns on and off alternating with the heating element being energized and not being energized. When the circ pump is running the heating element is not energized. When the circ pump is not running the element is energized. (the manual indicates this is opposite from the way it should be..it says "a safety switch prevents the unit from heating water unless the water is circulating") If anyone can confirm which is actually the way it's supposed to be I would appreciate that..and if it is operating backwards how that could happen.
Back to the diagnosis..The test program ends with a heater fault which would make sense if some part of the heating system was malfunctioning causing the unit to never continue past the water heating stage. I have checked the resistance of the heating element and it is at 11ohms as it should be so it's not bad. The next and last thing to replace on the heating system is the aqua sensor assembly. Is it likely this will fix the problem or is that going to be another wasted $30..?
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May 10th, 2012, 07:38 AM
#2
Hi,
With heater on (during test program), measure dishwasher incoming current (blackwire).
If ~ 11A, heater is working fine.
If ~ 1.5A, heater circuit has failedUse dishwasher test program to turn on heater, then measure dishwasher incoming current. If ~ 1.5A, heater, Hi-Limit, flow switch or circulation pump has failed. Check voltage @ module (or timer) --if 0V, module (or timer) has failed.For electronic models, current can also be measured through red heaterwire at control module (~ 9.5A). Since there can be more than one redwire, check wiring diagram to select heaterwire.
Flow through heater heats water without an exposed tank element. Filtered water enters the heater from the circulation pump. The heater heats water when the flow switch signals water is present.
The sump also contains an aqua sensor, drain pump, NTC, Hi-limit and backflow valve. The aqua sensor senses water cleanliness –dishwashers add rinses if needed. The NTC senses water temperature. The Hi-limit shuts off the heater if the water gets too hot. The backflow valve prevents waste water from entering the dishwasher.
The aqua sensor only affects energy usage, eliminating a pre-wash and/or pre-rinse cycle if water is clean. Most customers won’t notice if an aqua sensor fails.
Above is copies....hope it helps.
jeff.
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May 10th, 2012, 07:49 AM
#3
Originally Posted by
jeff1
The heater heats water when the flow switch signals water is present.
This also points to the possibility that the unit is operating completely backwards. When my circulation pumps comes on, you can see the black switch on the heater engage. When the switch engages, it cuts power to the right leg of the heating element (looking in from the right side of the dishwasher).
Let me make sure I have the basics right by asking this question...is the heating element on and heating when both legs test positive for 110V? And is it off when only the left leg tests positive for 110V?
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May 10th, 2012, 03:25 PM
#4
You have to check accross the two wires for the heater.
jeff.
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May 10th, 2012, 05:10 PM
#5
Originally Posted by
jeff1
You have to check accross the two wires for the heater.
jeff.
forgive me Jeff but I'm not sure what that means..I have a tester that you can just put near a wire and it will beep if 110v is going through it. The left wire on the heater has constant power and the right wire has power when the circulation pump is not running. When the circulation pump comes on the right wire loses power.
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May 10th, 2012, 06:37 PM
#6
forgive me Jeff but I'm not sure what that means..I have a tester that you can just put near a wire and it will beep if 110v is going through it.
That's not really a tester. A volt meter is...
jeff.
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May 11th, 2012, 04:30 AM
#7
I checked across the 2 ends of the heater for resistance and it measures 11ohms. According to the manual that means the heating element is OK.
Do you know why the element would be heating in a sequence opposite what is described in the manual?
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May 11th, 2012, 05:02 AM
#8
Do you know why the element would be heating in a sequence opposite what is described in the manual?
Nope.
I bought this dishwasher for cheap thinking all it needed was a circulation pump
Someone else was in there first and mixed up some of the wiring?
jeff.
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