Miele H4890 bp2 Oven heating weirdness

[ccg5f]

Double Miele Oven, model H4890 bp2 (electric), 7 years in use.  All menu diagnostics fine -- no error codes and fans work, doors latch, etc... Bottom oven works okay other than beeping that temps are reached at 6 mins and not actually reached until about 20 mins. But top oven set to 400 for bake or convection bake heats to around 350 then stops heating and cools--however, digital display shows oven continuing to heat, sometimes it says it reaches 400 but other times just continues to try.

 

Setting oven to other functions such as broil or roast works. For instance, setting oven to broil at 500 is reached in reasonable time. Then switching to bake at 400, oven will cool to 400 and maintain....something about attempt to heat from cold to above 350 in those two settings (primary ones needed) is the killer.  There is no certified Miele tech in my area and no other appliance repair wants to deal with a Miele. Miele itself says it may well be a control electronic unit -- which it will happily sell/deliver to me for over $1000 but if that doesn't fix problem, they will not accept return of part. Im a dyi person and dont mind attempting repair myself (actually did refrigerator control panel myself with soldering iron and tips from google), but Miele keeps unhelpfully tight lid on this mess.

Suggestions other than preheating via broil then switching to function actually needed?

Thanks!

 

 

 

[LI-NY Tech]

Miele does have a service bulletin for this model related to odd temps being caused by faulty power electronic software.  The updated software is only available with a new board.  However, first I'd test the temp sensor.  To do this you'll need an accurate temperature probe (like a Fluke 116 ).  Let the oven preheat on convection bake to 320*F for at least 30 minutes with the probe set somewhere in the center of the cavity, but not touching anything so you get a good air temp reading.  

Let it cycle a few times (if it will) and note the high and low temps on the meter.  Average them.  After 30 minutes the temp should be pretty stable so the displayed temp on the meter should be a suitable reference.

Also get into service mode, which I think you know how to do since you checked for error codes, and get into the sensor test menu and choose "temperature interior".  This will tell you what the electronic thinks the cavity temp is.  If it's way off you may have a bad temp sensor.  Miele doesn't give temp sensor resistance values so we don't have a way to directly test the sensor itself.

 

[Samurai Appliance Repair Man]

52 minutes ago, LI-NY Tech said:

Miele doesn't give temp sensor resistance values so we don't have a way to directly test the sensor itself.

Miele uses RTD sensors in their ovens (as do almost all manufacturers). All RTD sensors have the same temperature-resistance specifications so if you find a data table for one RTD, you can use it on all RTDs. Here's one:

[ccg5f]

Thanks so much for your help. I had to get my hands on a Fluke 116 with temp probe.

Set to convection 320:

@15 mins temp was 270 (display said 294)

@ 21 mins temp was 255 (display beeped notice that oven had reached 320 temp)

@23 mins temp started dropping (highest temp I noted was ~270)

@30 mins temp down to 233 and continuing steady fall. Display still showed oven at 320

 

In the sensor test mode the temp shows (readings over 5-10 mins)

Oven 176, fluke says 183

oven 185, fluke 189

oven 190, fluke 190

oven 198, fluke 194

 

[also checked temp catalyst at that point and it showed 163 (don't know what this is, but in case it's relevant)]

I would *really* appreciate any input--not sure what to do at this point.  Thanks!!

 

 

[ccg5f]

I had been thinking this issue was related to reaching a certain temp and then falling, but I now think it's time related. I just re-ran a convection test with cooled oven set to convection bake 340

 

@5mins oven 185, fluke 250.5

@10mins oven 263, fluke 310

@15mins oven 324, fluke 361

@16 mins oven 334 and fluke shows steady decline. Oven continues to show heat increasing and fluke shows steady drop (oven sensor temp check shows oven temp about 4-5 degrees off of the fluke)

could this be related to timing rather than temp related? And regardless, how to fix? This *|*{+{£ oven has always been under on temps by 25-50 degrees and I've always just set for higher than I needed. Display has also always beeped that oven has reached requested temp about 15-20 mins before temp actually reached.  (Likely didn't help that the "Miele Certified Installer" never set correct voltage setting--I just recently corrected voltage after customer service had me check it). But this now, I can't work with. 

 

Thanks again for any suggestions or help!

[ccg5f]

Anyone have any suggestions or tips? Would really appreciate it!

[weebles]

I know this is an old post but I have recently ran into an issue eerily similar to this.

Miele support said they have had issues with other models and indicated that the issue can be with the door switch. The plastic actuators age and as the oven heats up, the door micro switch is released as the actuator bends. This stops the heating cycle and the temperature yo-yo's well below set temperature but the control never indicates this.

Just something to look at.