Bosch SMV dishwasher - Tap light flashing and no heat

[loloop]

Hi all,

I am new here, so please be gentle.

We have a Bosch SMV40T10GB/35 dishwasher which is malfunctioning.

When a cleaning cycle is started(ECO 50deg) it seems to run as normal, and you can hear all the usual sounds such as water being splashed around and the drain pump running. But towards the end of the cycle it stops with an error beeping and the tap light flashing fast. The interior is not warm or hot.

1. I checked the drain hose and water inlet hose for bends - No bends
2. Checked and cleaned the water inlet filter - It was clean
3. Checked the float for any leaks - Cleaned all the door seals - Indication of previous leak(s) but not recent.
4. Checked the resistance of the heater pump (20ohm)
5. Checked the PCB (in door) visually for obvious burn marks.

I am still having the same issue. I am slowly running out of options.

Next I am thinking of checking the

1. Thermostat / Thermistor resistance check
2. PCB check in lower part

Do you have any ideas what it could be/what I could check for?

If you made it this far - Thank you for taking the time to read this.

Daniel

 

[loloop]

I found the culprit.
The thermistor on the heater element of the heat pump is broken.
Resistance test on the 2nd sensor has no resistance whereas the 1st sensor has a resistance at around 11-12k ohm.

Let’s hope a new pump will fix the tap error light as well.

Does anyone know if a thermistor in this can be fixed or do I actually have to buy the entire pump?

 

[jj4091]

Not sure if this https://www.espares.co.uk/product/es664217/dishwasher-thermostat is the part you need but they don't seem much cheaper than a complete pump. Not sure if stat/thermistor you require comes with a new pump so it might be a good question to ask before you order one

 

[loloop]

The heater element that needs replacing is actually this one, but it is not much cheaper that the entire heat pump assembly.
The part is actually this little thermistor here (circled in red) that is broken.

Feels like a shame to replace the entire heat pump because a little thermistor is broken.

 

[Harry Bloomfield]

With nothing to lose, might it not be worth a try - digging into where the thermistor is located, soldering one on to its leads, then sealing it with araldite? Thermistors can be had for just pennies.

 

[SpecialK]

Are you sure they are not high and low thermistors or something - hard to know without a drawing etc....? Have you connected a multimeter to the heaters power to see if it gets anything when the dishwasher is run and should be heating? I would also remove the PCB and ensure the relay powering the heater is working correctly and low resistance across its contact. Not a bosch dishwasher but the contacts burnt up on mine causing no heating.

 

[loloop]

According to this video I should get a resistance reading for the sensors.
I’m getting the 11Ohm for the first sensor but nothing on the second or as in the video nothing when combined.
I’m not sure why there are 2 thermisitors.
I think I will struggle to find out exactly which thermistor this will require unless I find a diagram or find a spare identical model and use thermistor.

 

[Harry Bloomfield]

I’m getting the 11Ohm for the first sensor but nothing on the second or as in the video nothing when combined.

I suspect you meant 11K Ohm? Actual resistance, varies with temperature...

Likely, this will be a direct replacement, for the failed component, if you can access it - NTC 10K https://cpc.farnell.com/vishay/2322-640-63103/thermistor-ntc-10k-5/dp/SN35070

 

[loloop]

Yes, indeed I meant 11k Ohm.
Just out of interest, how do you know it is this thermistor? Other than the resistance reading.

 

[Harry Bloomfield]

Yes, indeed I meant 11k Ohm.
Just out of interest, how do you know it is this thermistor? Other than the resistance reading.

A 10K at 20C is a the most commonly used thermistor.

 

[SpecialK]

Just replace the whole unit it to save the washing piling up! Sounds like your diagnosis is correct according to that video...

 

[loloop]

I am losing my mind!
We have been running cold cycles to clean the dishes and then washed the stubborn dirt off after in the sink. We ran a cycle today and a couple of hours later when I emptied it it was warm?!
So, I checked the thermistors resistance again and I got a reading on both.
I’m running a hot cycle right now and the dishwasher is hot! WTF?

 

[Harry Bloomfield]

I’m running a hot cycle right now and the dishwasher is hot! WTF?

Poor connection, fixed by unplugging and reconnecting?