Coffee maker repair

Thread Starter

RenMcCourtey

Joined Dec 11, 2018
8
Hi, I have this coffee maker, which is basically your usual filter based dripper, only equipped with a mill, so you have freshly ground coffee each time. It is able to boil exact amount of water you set, saying you select 6 cups with buttons, pour water to the 6 cups mark and it boils water exactly until the tank is empty. It was running nicely for about two years after which a limescale removal was needed. I used generic acidic mixture sold for exactly this purpose. Immediately after that the machine went haywire, right now it never boils out all the water, leaving random amounts of water in the tank.
Now, I was thinking about how these recognize the time required to boil, had two ideas in mind: timer, factory preset like 120s for 2 cups, 180s for 3 cups, etc...but that doesn't seem to be very dependable, considering very different conditions the machine can operate in. But a dead capacitor in the timer would explain erratic behavior. The other idea is some kind of simple sensor down the boiling tube, to detect if water still comes from the tank or not. This seems to be more likely to me, especially considering it stopped working properly after using the cleaning liquid, sensor could get damaged. I'm generally able to fix many home appliances but here I am totally lost. After disassembling most of the maker I could not find any clues, not even sure if the cleaning process is a culprit or it was just a coincidence. Does anyone have an idea what should I look for?
 

MaxHeadRoom

Joined Jul 18, 2013
23,632
Generally they posses a thermal sensor that detects when the water tank is empty, i.e. shuts of the boil, it then goes into lower heat mode in order to keep the perked amount hot.
Max.
 

drc_567

Joined Dec 29, 2008
1,154
... Look around for a 'thermal fuse'. It may be located external to the boiling chamber someplace. These frequently wear out or fail somehow, and could be the cause of the difficulty. If you find a likely part, examine it for numbers indicating the switching temperature. Replace with an identical part. ... Solder may be required for correct installation. ... A heatsink on the fuse capsule is sometimes necessary when soldering the lead wires.
 

MaxHeadRoom

Joined Jul 18, 2013
23,632
... Look around for a 'thermal fuse'. It may be located external to the boiling chamber someplace. These frequently wear out or fail somehow, and could be the cause of the difficulty. If you find a likely part, examine it for numbers indicating the switching temperature. Replace with an identical part. ... Solder may be required for correct installation. ... A heatsink on the fuse capsule is sometimes necessary when soldering the lead wires.
I think the OP has an issue with the heater element shut-off (thermostat) , not the thermal fuse, which blows if the element does not shut off via the thermostat.
Max.
 

drc_567

Joined Dec 29, 2008
1,154
Maybe the first thing to check out would be to make sure that the thermostat mentioned above is making effective thermal contact with the heating tube or chamber. A dab of thermally conductive compound might eliminate the random heating that was mentioned.
 

Thread Starter

RenMcCourtey

Joined Dec 11, 2018
8
OK, ok, I'll start with removing the bottom again, to reach the heating element, making some pictures this time. We'll see what parts are present, will also check the proper thermal contact. So far, as I understand, it seems to be unrelated to the cleaning in any case, right?
 

wayneh

Joined Sep 9, 2010
17,153
OK, ok, I'll start with removing the bottom again, to reach the heating element, making some pictures this time. We'll see what parts are present, will also check the proper thermal contact. So far, as I understand, it seems to be unrelated to the cleaning in any case, right?
No, it could still be related to the scaling and cleaning. There may be a thermal sensor inside the water reservoir. Or it could be the water level sensor that I believe that model has. The good news is that descaling may have merely been inadequate and you have a big hunk of scale buggering the sensor. You need to get in there and see.
 
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MaxHeadRoom

Joined Jul 18, 2013
23,632
All the ones I have come across do not have a level sensor, per-se, you fill it to the No of cups you need and then it boils off the water until the reservoir is empty, the thermal sensor shuts off and then goes in to just heat the coffee pad mode.
Max.
 

wayneh

Joined Sep 9, 2010
17,153
All the ones I have come across do not have a level sensor, per-se, you fill it to the No of cups you need and then it boils off the water until the reservoir is empty, the thermal sensor shuts off and then goes in to just heat the coffee pad mode.
Max.
I looked up the manual for what looked like this model, and it mentions a level sensor. That raises an eyebrow. The Bunn machine I’m repairing for a friend has nothing so clever but it does have a thermocouple or whatever type that sensor is. I think the volume is controlled by simply cutting off a natural siphon effect once the reservoir level falls enough to break the siphon. Simple but elegant.
 

killivolt

Joined Jan 10, 2010
800
I use Distilled water in mine because the water in Utah is very heavy mineralized. Once I replace the water heater, I’ll install a Reverse Osmosis system with UV Light.

This reminds me of repairing them back in the day when we were a repair vs throw away society. I do like knowing something isn’t going to the dump.

kv
 

Thread Starter

RenMcCourtey

Joined Dec 11, 2018
8
OK, so this is what's in the bottom. Boiling element is clearly separated from pad heating, being connected with red (marked HOT on PCB), black (marked NI) and white (WEN on PCB) (also there's the obvious ground wire). There seems to be no simple way to pull the element out to look for thermal sensor, without dissembling the body more.

Also, there is another (probably just cosmetic?) issue which started at the very same time. Quite a lot of humidity inside while boiling builds up as a water droplets in front of LCD, weird but this never happened before. Around of electrical parts at the bottom it is perfectly dry and clean though, no leaks.
 

Attachments

AlbertHall

Joined Jun 4, 2014
11,505
There is clearly moisture getting to the electronics as shown by the display. Water and electricity are not a good mix. This may be the root of your problem. Water or steam is escaping somewhere in there and needs fixing.
 

Thread Starter

RenMcCourtey

Joined Dec 11, 2018
8
There is clearly moisture getting to the electronics as shown by the display. Water and electricity are not a good mix. This may be the root of your problem. Water or steam is escaping somewhere in there and needs fixing.
Generally I do agree, of course, but in this case is the control panel with LCD situated directly above the filter chamber and there is even vapor vent located directly next to it. All the other electric and electronic components are located in the base of the appliance. I can't really imagine this wouldn't be accounted for. I even tried to completely dry out the whole appliance for a week or 10 days, and immediately the first brew had wrong amount of water, before this moisture got built up again.
 

Attachments

drc_567

Joined Dec 29, 2008
1,154
There is no obvious indication in the photos of a thermal fuse or thermostat sensor.
It may be that the current magnitude going through the heating element in the boiling chamber is monitored or sensed by something. As the water within the boiling chamber, in the immediate vicinity of the heating element, actually turns to vapor, there should be an increase in temperature causing the heating element to have increased resistance ... essentially because the boiling vapor zone is not able to conduct heat away from it nearly as well as the liquid phase water.
The resulting increase in the heating element resistance causes a decrease in current, which is then monitored electronically by some means ... Maybe on the pcb board someplace.
So if the defect is too much heat ... The heating element not shutting off at appropriate levels, or just erratic current control, the problem may be with the heating element current sensing part, whatever that may be.
... No obvious correlation with the cleaning process that was mentioned at this time.
... A guess at best.
 
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AlbertHall

Joined Jun 4, 2014
11,505
Generally I do agree, of course, but in this case is the control panel with LCD situated directly above the filter chamber and there is even vapor vent located directly next to it. All the other electric and electronic components are located in the base of the appliance. I can't really imagine this wouldn't be accounted for. I even tried to completely dry out the whole appliance for a week or 10 days, and immediately the first brew had wrong amount of water, before this moisture got built up again.
Those buttons are in the same region as the display. Are they completely waterproof?
 
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