Hello All!

I bought a used Oscar a while back, fixed a couple of leaks and installed a vacuum breaker, and have been enjoying great espressos ever since...

...until today.

When I turn on the machine, the pump starts and does no stop. Water (eventually hot) is slowly coming out of the hose on the neplax side (left) into the drip tray. I see some water/bubbles in the other (right side) hose as well. When I turn on the portafilter valve (button), water exits there normally.

I (probably stupidly) tried to close off the hose on the neplax side to test to see if that valve was indeed the problem. I was able to diminish the water flow quite a bit, but the pump still never stops and more water seemed to come out the right-side hose instead.

Any ideas?

Thanks!

matt

Pump running on power-on is generally a dirty boiler level probe or a consequence of running water with zero mineral content for an extended period of time. Do you get water out of the steam wand when the pump is running like this? If so, I would open the top cover and remove the wire attached to the level probe and temporarily hold it against the surface of the boiler and power the machine back on. If the pump continues to run, you have an issue with the auto-fill control circuit. If the pump calms down, remove the level sensor and give it a good scrub.

Since you installed a vacuum breaker, I'm sure you know where the level probe lives, but just in case there's a good photo of it in this post.

Cheers!

- Jake

Jake,

Thanks so much. There is some water coming out of the wand and the (open) vacuum breaker at power on (and pump running), but steam too.

I removed the level probe connection and held it against the boiler side. The pump did not stop. Based on your post, this seems to indicate the control circuit.

Let me throw out one other scenario, however. As a test, I disconnected the pump (only) and let the system heat up. Once hot (light went out), I re-connected the pump and it did *not* come on. I can pull a shot (pump comes on). When I turn on the steam wand, however, the temp light goes on and the pump starts again. Does this change at all what you are thinking?

Appreciate all your help.

-matt

mcnowinski wrote: I removed the level probe connection and held it against the boiler side. The pump did not stop. Based on your post, this seems to indicate the control circuit.

Let me throw out one other scenario, however. As a test, I disconnected the pump (only) and let the system heat up. Once hot (light went out), I re-connected the pump and it did *not* come on. I can pull a shot (pump comes on). When I turn on the steam wand, however, the temp light goes on and the pump starts again. Does this change at all what you are thinking?

This is an odd combination of events. It could be that I don't understand how the level probe in an Oscar works and that grounding it to the boiler won't trick it into thinking the boiler is "full". It could also be that the exterior of your boiler is not providing a good path to ground for your level sensor.

In either case, I would recommend removing the level sensor and cleaning any scale or tarnish off the surface of the probe. Buildup on the probe will prevent it from detecting water in the boiler. This is the most simple and easy to resolve cause of your problems and would be good to rule it out before trying more exotic troubleshooting.

Cheers!

- Jake

OK. Removed an cleaned the level probe just in case. Water level in the boiler actually looked good. Tested conductivity of boiler to ground and that looks good too. I think the boiler is actually filling correctly (I can hear the relay for it click on occasionally), but the pump still runs continuously at power on pushing water (most of the time) slowly through the group head (and out the neplax valve).

As I mentioned, I hacked the electrical connection to the pump to allow the machine to heat all the way up without turning on the pump (i.e. disconnected power to the pump). When I reconnect pump power *after* pressure stat says everything is good (i.e. heating status light is out) the pump does *not* turn on.

Any idea how/why the pressure stat is linked to the pump power? I will try to dig up the electrical diagram.

Finally , wen I open the steam wand, the pressure drops, the heat light comes back on, and the pump starts again until it comes back up to pressure.

I purchased a new neplax valve, but I am not sure how a leaky neplax valve could be related to the pump issue.

Thanks to all for your help and patience.

matt

mcnowinski wrote: Any idea how/why the pressure stat is linked to the pump power? I will try to dig up the electrical diagram.

I'm trying to figure out how that's even a possibility... I would defer to @Bluesman, @plindy or another Oscar specialist for the working details, but the schematic can be found here.

mcnowinski wrote: I purchased a new neplax valve, but I am not sure how a leaky neplax valve could be related to the pump issue.

It won't help. But it won't hurt to have a new valve, either. Looking at the wiring diagram, I can't see any way other than an issue in the brain box that this could be happening. Even then, there is no single failure point I can identify that would give you the symptoms you have. The pressure stat gets its neutral from pin 5 on the board, which completes the circuit and powers the element. Pin 7 sends neutral to the pump when auto-fil is activated, as does the the brew switch which is working correctly...
Is the low water lamp illuminated when the pump and heating element are on together or just the element lamp?
I can't find a smoking gun yet, bit I'll keep scratching my head!

Cheers!

- Jake

Ok,
I have a pretty solid understanding of the schematic now.
Here's a list of what's on the controller with my interpretation of function:

1:Reservoir level input - continuity with pin 3 through level switch when level is ok.

2:Boiler level input - continuity with pin 3 through boiler level sensor and boiler ground wire when level is ok.

3:Chassis ground, splits to boiler ground, reservoir level switch and ground for both solenoid valves.

4:Neutral supply to brew switch - switched continuity with pin 10, controlled by pin 1, (and maybe pin 2?)

5:Neutral supply to pressurestat - switched continuity with pin 10, controlled by pin 1, (and may be 2?)

6:Neutral supply to boiler-fill solenoid valve - switched continuity to pin 10, controlled by pin 2.

7:Neutral supply to pump - switched continuity to pin 10, controlled by pin 2.

8: 120V (230V) supply to controller - switched power supply from main power switch by way of heating element and pump. External jumper supplies constant 120V to both solenoid valves and all 4 indicator lamps.

9:Neutral supply to low water lamp - switched continuity to pin 10, controlled by pin 1.

10:Neutral supply to controller - switched neutral supply from main power switch with external jumper feeding on-off lamp.

Having this all laid out in front of me, it seems likely that the issue is with pin 5, inside the controller. If there is water in the reservoir, pin 5 should supply neutral to the pressurestat through pin 10 (maybe not if the boiler level is low?). Instead, it appears that when the pressurestat closes, it is somehow supplying a path for electricity to flow from the pump motor through pin 7, which should only be possible when pin 2 doesn't sense water in the boiler...

Quick question: Is this machine on a GFCI outlet?

A diagnostic test you could try would be to disconnect the pressurestat from pin 5 on the controller and hook it up to pin 10 directly. This would give the heating element a direct neutral line, bypassing any switching in the controller. If the problem goes away, this points to a problem with pin 5 the controller. If the problem persists, more digging is necessary. See testing scenario below: Don't electrocute yourself.
Remove the wire represented with the red line from pin 5 and jumper it onto pin 10, along with the existing wire already on pin 10 as depicted with the blue line. Please be careful and unplug the machine before swapping wires. Test to verify pin 10 is actually supplying neutral and that the schema is correct before trying this, as well. Remember, running the machine in this manner defeats any safety in the controller to prevent the heating element from running with a dry boiler. Don't run the machine like this.

Good luck!

- Jake

all things Oscar

sounds like several conditions

be careful removing neplex no room

use sealent , threadlocker , for installation

there is a mold line on the group head , and only 4 threads for securing the neplex , not too tight...

study Gianni's tips page , link above

confirm 3way , and 2way , 1way valve in HX return line , and wiring to power and brew switches

after that it get's more involved

condensers , relays , transformer , ic chip , on brain box can fail , however
usually not with the symptoms you describe

Gluck

Thanks to all for your comments.

Jake, wow, this is such good detective work. I will take a look at the schematic and try your test.

Also, this system is indeed on a GFCI. Do you think this resulted in some type of damage to the controller?

Thanks. Back soon !

matt

mcnowinski wrote:Thanks to all for your comments.
Also, this system is indeed on a GFCI. Do you think this resulted in some type of damage to the controller?

Thanks. Back soon !

matt

Negative on controller damage. I was just looking at the schematic and trying to identify a way for the pressurestat to engage the pump. Any scenarios I could cook up would result in current leaking to ground, which a GFCI would detect and trip .

plindy wrote:all things Oscar

Excellent resource here, although I don't see your problem called out...
Let us know how it goes!

-Jake