Bezzera BZ02 (Livia 90) Won't Cycle Off

Postby danno on Fri Jan 28, 2011 8:41 pm

Hello All-

Early this week, I had to use my Bezzera BZ02 at work for hot water (appx. 8oz each time) for three days in a row. On the third day, later in the day, I made my afternoon shot of espresso and noticed that the pressure gauge kept rising beyond its usual 1.1bar. The heating element overheated and the safety switch tripped.

The machine is now home with me. I reset the heating element: It works fine. The pump works fine, too. The machine heats up, the valve on top of the boiler closes when it should, pressure develops, but then it keeps developing. It does not stop. It keeps getting hotter and hotter until I assume the heating element will shut itself off once again. I haven't gone that far yet.

I thought it might be a pressurestat issue, so I took the pressurestat off (a replacement CEME unit) but it looks perfectly clean inside. That is not a scientific test, so I fired up the machine again and tried disconnecting the pressurestat manually to see what would happen. When I disconnected the presurestat, the boiler continued to get hot and pressure continued to build. The pump was not running. I could hear a relay click on the opposite side of the machine when I disconnected the pressurestat. Am I going about this completely wrong?

The machine evidently overheated when I used it for hot water: The pump and element were running for almost a minute after my last use. I cannot see any burnt wires, and all the obvious components seem okay.

Can anyone steer me in the right direction as to what might be the problem with this machine?

TIA!
-Daniel
User avatar
danno
 
Posts: 126
Joined: Sep 09, 2005
Location: Stuttgart & Atlanta

Postby another_jim on Fri Jan 28, 2011 11:17 pm

Does the machine have a solid state relay or contactor to switch the heater? If the heater is higher than 1100 watts, it's amperage at US voltages is too high for the Ceme's 10 amp microswitch. In that case, it may be that element that is frozen to the on state.
User avatar
another_jim
Team HB
 
Posts: 9112
Joined: May 05, 2005
Location: Chicago

Postby cannonfodder on Sat Jan 29, 2011 9:40 am

Pressurestats can be tricky. It may look good but the membrane could be stiff and not flexing. You could try taking a small round, not sharp object and gently poke the diaphragm in the pressurestst. It should flex/pop up and down. If it does not, it is stuck. As Jim suggests it could be welded together contacts in the pressurestat, or if it has a SSR, it could be a fried relay but the pressurestst is the usual culprit. You can try putting some vinegar in the pressurestat and let it sit for a few hours to see if that cures it.

Pressurestats are subjected to 250 degree steam, high pressure and high voltage all day, every day. Frankly it is amazing they last as long as they do. They are relatively inexpensive, I usually keep one along with a vacuum breaker and group gasket in my spare parts drawer.
Dave Stephens
User avatar
cannonfodder
Team HB
 
Posts: 7942
Joined: May 23, 2005
Location: Downingtown PA

Postby danno on Sat Jan 29, 2011 11:18 am

another_jim wrote:Does the machine have a solid state relay or contactor to switch the heater? If the heater is higher than 1100 watts, it's amperage at US voltages is too high for the Ceme's 10 amp microswitch. In that case, it may be that element that is frozen to the on state.


Hey Jim-

I am not 100% sure what you mean by "contactor." My machine uses a set of mechanical relays to control the heating element:

Image

The upper black box appears to be a relay and the bottom one definitely is one. It seems to be the one that controls the heating element. Are you suggesting that it is fused on? I think the BZ02 has a 1200w element.

I checked the pressurestat internally and its diaphragm is fine—assuming I did not mess it up by poking it! :) Bypassing the pressurestat pretty much convinced me that it was not the problem already.
User avatar
danno
 
Posts: 126
Joined: Sep 09, 2005
Location: Stuttgart & Atlanta

Postby erics on Sat Jan 29, 2011 11:36 am

If you're absolutely convinced that the pressurestat is NOT the problem, then the only other device that would initiate a "runaway" heating element is the clear relay you show in your pic. The "black box" is very likely the Gicar box which handles the boiler autofill function.

Bezzera later located this relay alongside the pstat in their BZ07 models. Depending upon your electrical know-how (and assuming this mechanical relay is at fault), it may be worthwhile to replace this mechanical relay with a properly configured SSR.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at erols dot com
User avatar
erics
 
Posts: 4522
Joined: Aug 09, 2005
Location: Silver Spring, MD

Postby danno on Sat Jan 29, 2011 5:11 pm

I took the mechanical relay off and disassembled it. From an un-scientific and entirely empirical observation, I suspect it was the culprit:

Image

:lol:

Luckily the contacts were the only affected part, the coil still works fine. The contacts obviously got very hot when left closed (on) while the machine was refilling and re-heating after I used it for hot water. I cleaned the contacts and the machine is working again, cycling on and off between 1.0 and 1.3bar.

This is a temporary solution. I already sent out one email inquiring for a replacement relay. I am unfamiliar with SSR's as Eric mentioned. Can anyone guide me through this? I am competent with electronics but have never tried such a thing before. I am willing to try if it seems reasonably easy and not too expensive. Otherwise, a replacement relay is fine as long as I can find one and it is not exorbitantly expensive.

Thanks!
User avatar
danno
 
Posts: 126
Joined: Sep 09, 2005
Location: Stuttgart & Atlanta

Postby erics on Sat Jan 29, 2011 5:29 pm

Judging from the lack of real estate available in your first pic, a replacement relay is your best overall bet. Depending upon your machine's production date, this looks like the appropriate relay:

http://www.1st-line.net/cgi-bin/category.cgi?item=7635418&type=store

You may be able to find an identical replacement part elsewhere (its probably a Finder relay) but that will take a little detective work.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at erols dot com
User avatar
erics
 
Posts: 4522
Joined: Aug 09, 2005
Location: Silver Spring, MD
kshanticoffee.com: we love to make things and we also love coffee
kshanticoffee.com: we love to make things and we also love coffee

Postby another_jim on Sat Jan 29, 2011 8:37 pm

It looks like the relay has a second pole. If it does, you're ready to go; since that pole will be good as new.
User avatar
another_jim
Team HB
 
Posts: 9112
Joined: May 05, 2005
Location: Chicago

Postby danno on Sun Feb 06, 2011 7:01 pm

As Jim noted, the relay does have two poles to the switch. It appears that the machine uses both of them, though: The wires are run in parallel (or maybe series, I guess it depends on how you think about it) across them.

I cleaned up the original relay and everything worked fine, but for the sake of safety and preventative maintenance, I used Eric's link and got a replacement relay. All is well once again. Whew! I now know not to leave the Bezzera running that long when reheating after filling up a cup with hot water. I should have known better!
User avatar
danno
 
Posts: 126
Joined: Sep 09, 2005
Location: Stuttgart & Atlanta

Postby Michael Mack on Mon Feb 06, 2012 4:52 pm

took a while to sort this problem, overheating & no water to the coffee dispenser. thought it was the mechanical relay as it looked the same as the one in the photo, cleaned it works fine. removed & checked the pressurestat, this works fine also. turned out to be the pipe to the coffee dispenser was blocked.. all seems ok.. so far.
Michael Mack
 
Posts: 1
Joined: Feb 06, 2012
Location: UK