Siemens dryer iQ800 WT48Y780EU

[jm1234]

Hi,
I'm looking for ideas on how to aproach this, I spent many ours already.
The dryer doesn't get hot, only warm and then gives error E25 (Fault with the sensor or electronics detected).
Now I'm testing it using the service mode - it gets the temperature of the heat pump liquid to 52C and then it stops the heat pump. After few minutes it then produces E25.
I tried to understand if it stops the testing because the final temperature was reached and I don't think that's true. While it was running, I heated that sensor using hot air to 80C and then it stopped. So I think the heat pump never reaches the right temperature (why also clothes never get hot).

Topology is:
- front panel (probably not an issue)
- invertor board (IKCS17F60F2A, big capacitor, big inductors etc)

- main board


I already changed the main driver chip for the heat pump motor IKCS17F60F2A and also the largest capacitor on the invertor module. That didn't help.

I admit it is pretty difficult for me to do any measurements on those boards while their powered on, but I can try to solder wires for that.
The service test results don't show much as far as I can tell, see the attachment. The high temperature sensor seems to be working fine - I can see its measurements on that service screen.


Any idea appreciated.

[CapLeaker]

While an E25 error on a regular dryer is the sensor, I think in this one (heat pump dryer) it is a problem with the electronic board(s). Do some checks on the relays and see if maybe one is bad. At least it is that way with Bosch dryers, so I think Siemens should be the same.

I found a thread having the exact same symptoms and the big capacitor on the PSU was the problem. Check it out.
https://www.iwenzo.de/threads/siemen...icht-an.73047/

[jm1234]

While an E25 error on a regular dryer is the sensor, I think in this one (heat pump dryer) it is a problem with the electronic board(s). Do some checks on the relays and see if maybe one is bad. At least it is that way with Bosch dryers, so I think Siemens should be the same.

I found a thread having the exact same symptoms and the big capacitor on the PSU was the problem. Check it out.
https://www.iwenzo.de/threads/siemen...icht-an.73047/

Thanks,
quite interesting that it's usually that big capacitor, I was certainly hoping replacing it would help, but no luck. I also previously tried all the relays and they seemed fine - I was able to turn them on by supplying voltage on the coil. How do you think a faulty relay would cause this issue? I would expect a faulty relay to not switch at all, or even be shorted, that I already saw. I admit I haven't seen much :-).
Anyhow, I tried to run the test again, it went to 48C and the compressor stopped. Then I tried to start the same test again immediately and the compressor didn't even start. As if some state was reached that prevents it from running. If I wait few more minutes, I would be able to run it again. It's not the (high) temperature I'm sure. Is there a low temp sensor?
I wish I had the service manual for this unit
Thanks

[CapLeaker]

Thanks,
quite interesting that it's usually that big capacitor, I was certainly hoping replacing it would help, but no luck. I also previously tried all the relays and they seemed fine - I was able to turn them on by supplying voltage on the coil. How do you think a faulty relay would cause this issue? I would expect a faulty relay to not switch at all, or even be shorted, that I already saw. I admit I haven't seen much :-).
Anyhow, I tried to run the test again, it went to 48C and the compressor stopped. Then I tried to start the same test again immediately and the compressor didn't even start. As if some state was reached that prevents it from running. If I wait few more minutes, I would be able to run it again. It's not the (high) temperature I'm sure. Is there a low temp sensor?
I wish I had the service manual for this unit
Thanks

A bad relay still could click and appears to work, but the contacts could be bad showing a resistance or open when the relay is on. It also could be making good contact only sporadically and not always. I assume the condenser is clean, could also be something with the charge of the heat pump unit, the compressor or the over current protection on it. Check the electrical isolation of the compressor (windings) and the over current protection on the plug if the compressor.

[jm1234]

A bad relay still could click and appears to work, but the contacts could be bad showing a resistance or open when the relay is on. It also could be making good contact only sporadically and not always. I assume the condenser is clean, could also be something with the charge of the heat pump unit, the compressor or the over current protection on it. Check the electrical isolation of the compressor (windings) and the over current protection on the plug if the compressor.

I hear you and I'm taking notes :-) However, the whole thing behaves pretty deterministicly, so there doesn't seem to be any element of chance. So I'm 99% sure we can rule out a random (relay) contact issue that would make it sometimes work and sometimes not.
As for the over current protection, my understanding is the big driver chip is feeding the compressor directly, so that logic is hidden to me. There are some feedback outputs from the chip though - would that be where the protection logic could be around?
VRU, VRV, VRW (low side emitter, Pin 12, 13, 14) in https://www.mouser.sk/datasheet/2/19...86-1168516.pdf

[CapLeaker]

Interesting… it has a fault pin. Check it!

[redwire]

German forums have more discussion about repairing the Siemens iQ800 (it also goes under a Bosch model as well).

One guy tore it apart and found the heat exchanger plugged with hidden dust. Did you check yours, way at the bottom? It might be heating up and the unit goes into shutdown.

The Component Test Mode display, bottom line I think is the analog values (as 8-bit ADC values 0-255). I think you'd have to scale them to read say a temperature sensor value in C.
It apparently uses 5k ohm thermistors for temp sensors.

[jm1234]

German forums have more discussion about repairing the Siemens iQ800 (it also goes under a Bosch model as well).

One guy tore it apart and found the heat exchanger plugged with hidden dust. Did you check yours, way at the bottom? It might be heating up and the unit goes into shutdown.

The Component Test Mode display, bottom line I think is the analog values (as 8-bit ADC values 0-255). I think you'd have to scale them to read say a temperature sensor value in C.
It apparently uses 5k ohm thermistors for temp sensors.

Thanks for the pointer, I just posted my question on that german forum. Yes I teared the whole thing down first thing and cleaned the radiator. But that didn't change anything so I proceeded to check the electronics.
As for the values on that test mode screen, some of those seem to be direct temperature readings. Specifically that TMP value is taken from the sensor that is directly on top of the compressor. That's the one I was heating up with hot air to understand if the dryer is stopping because it's hitting the max temp. Apparently not.

[CapLeaker]

Thanks for the pointer, I just posted my question on that german forum. Yes I teared the whole thing down first thing and cleaned the radiator. But that didn't change anything so I proceeded to check the electronics.
As for the values on that test mode screen, some of those seem to be direct temperature readings. Specifically that TMP value is taken from the sensor that is directly on top of the compressor. That's the one I was heating up with hot air to understand if the dryer is stopping because it's hitting the max temp. Apparently not.

could you upload a straight shot, high resolution picture of the power supply? So we can really see something? This one above isn't much good, as it is on an angle and has dark spots.

[jm1234]

Took 2 shots, because the high components are blocking the view.
Note: the wire thingy there is a substitute for one leg of the driver chip - it came from China broken, so I had to improvise. However, the overall behaviour didn't change, so I might as well put the original chip back.

[CapLeaker]

Hmm… and if you disconnect a sensor it won't run at all, right? Maybe measure the resistance on the sensors? It's a good head scratcher… for sure. The 2 caps close to the heat sink are good?
heat pumps don't turn on right away after you just turned it off. There is a delay. The thermo sensors shout read like 4.8kohm. I'd take a look at the compressor itself. This being said, I read multiple threads similar with your issue and it was always that the dryer was fixed after replacing that power supply board.
Why it fails I got no idea. Other tried to meter around, but never found anything much besides that big capacitor.