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

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.

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.

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:



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.

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





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!

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.

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!

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.