Bezzera BZ07 high limit tripping after a few minutes

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by alvi72 »

Hi all thanks for the great forum and all the information I have already found and used but I need some more and hopefully somebody can help me out.

The problem
After I turn the BZ07 on it heats up, builds up pressure, the relay clicks off again but within a few minutes it will trip the high limit switch

What is good
It turns on and you can hear the relay click to provide power to the element after which it will heat the water.
After the water is warm it will build up pressure to about 1.25 bar and it will produce steam.
It does provide provide warm water through both hot water tap and the brew head (which is evenly distributed across the head).
Once the 1.25 bar is reached the relay will shut off power to the element by switching relay
When the pressure drops it will switch the relay again to try and heat the water. (by this point the high limit was tripped already so no pressure was build up again)

What I have done
The original problem was both the high limit tripping and no water coming out of the group head.
So I have descaled the system. First by flushing it through the system and later by disassembling and cleaning the solenoïdes (brew valve and brew fill valve) and opv (took this completely apart).
I have replaced the pump priming valve as this cracked off while trying to disassemble the machine.
checked continuity on the element and the high limit switch (all of which seemed to be ok)
cleaned the contact area of both the bottom and contacts of the high limit switch.
Checked the continuity of the pressure stat (which was oke and changed at the right pressure) ( I have not taking this one of nor cleaned it as it seems to be working correctly)

What I think I know
Research on this site seems to point to the pressure stat and/or the controller as the most likely culprits for this problem

What I want to know
Have I missed anything that could be the problem?
How likely is the pressurestat the/an actual problem?
I hope that i do not have to replace the controller as that is an expensive part to replace, could there be an other problem resulting to the high limit tripping?
Is there an electric diagram for the machine and what could i still test on voltage and continuity?
any other suggestions of what i might have missed?