I'm currently borrowing a nice little VBM while my kitchen is being renovated rendering my own plumbed in coffee machine unusable.

The VBM works great for a couple of hours but then the pump will not switch on by toggling the brew lever.
I remove the VBMs rear cover and within a minute it works fine, put the cover back and after 10 mins it's not working.
Recently it's been relatively cold here so it's worked all morning with the cover on but later it the day it stops working - remove rear cover and it works fine.
I've been told it's a known problem due to a sensor (Thermistor?) issue but though I'd check with the VBM repair cognoscenti before I start tearing it apart as this may save me a lot of troubleshooting time.
I've had a look on the web for this problem but either my search skills are not good enough or I'm not using the right terms or there is no info on this problem,
Many thanks

Hi RobertoL VBM's are incredible machines!

Depending on your VBM, here's a Home-Barista post that might be similar to what you are describing perhaps? VBM Junior HX - wire with sensor? attached to ULKA pump

Again depending on the VBM model (sounds like its a vibration pumper), here's a photo of what a "Thermistor" might look like when in its pump-housing (circled in green, some are bonded in place with a white mastic or some similar soft adhesive)


If the pump is shutting down due to over-heating, this is a correct safety feature. The question will be why is the pump over-heating. On the side of the pump, there should be a duty cycle listing (something like 1/1 or 1/2 meaning 1 minute on/1minute off, or 1 minute on/2minutes off etc.). If the pump is overheating despite not being on, the Thermistor could be developing a fault or the pump components (the coil or diode) might be causing overheating and tripping the automatic Thermal cutoff fuse . . . again assuming a vibratory pump in use while your non-plumbed-in-renovation journey underway.

If this automatic thermal fuse is slipped out of its pump-housing it will not be in contact with the side wall of the pump coil and thus free of heating . . . however, this may result in the pump continuing to heat up to the point of permanent failure of the coil or diode in the pump. Its worth considering that that if the thermal cutoff fuse (thermistor) is shutting the pump down, this is a safety feature to protect the pump components and machine . . . and the house around the machine. A pump should usually only be on/run a minute or 90 seconds if that sounds right for the current usage amount. Many machines will automatically shut the pump off after 90 seconds. If the Pump gets too hot, the automatic Thermal Cutoff Fuse will open the circuit and de-energize the pump until the Thermal Cutoff Fuse cools enough to close the circuit and allow current to pass again so the pump can be energized.

Any photos you might have when you get a look inside would be of great assistance to others in future who also read this post and any details of this model of VBM will also assist in narrowing the components involved

Another possibility is the control box is failing when it gets warm.

It won't hurt to run the machine with the cover off - provided there are no curious little fingers about - to get through the remode.

Thanks so much for the all feedback.

Yes it is a vibe pump.
Not sure of the model etc as I can't find any markings on it
It looks like this

I think it's a Domobar Junior?

The pump doesn't stop mid flow - it just occasionally fails to start.
What's weird is sometimes by repeatedly toggling the brew lever the pump will start after 2-3-4 attempts, but sometimes it wont start after even 20 attempts.

When I say it works with the cover off I meant the top and the back/sides off. Now I have back/sides "on" and top off and see what that does.

I've had the back cover and top on for 24 hours and cant get it to fail. Mind you it hs been colder than usual here I will try and force the issue by covering the venting holes in this top.

Sounds like maybe a poor connection. You could try giving them all a wiggle or two WITH THE MACHINE UNPLUGGED!!

Can't recommend overheating the innards by blocking what minimal ventilation there is.

Thanks for the feedback The machine has had its back and top "on" for about two days and has not failed. Also has ventilation holes blocked off for most of a day and has not failed. I've unblocked the holes and will have to wait till it fails again.

OK finally it failed again (with top and back on) and within minutes of removing top it works again. Rather than mangling the original top I. thinking of fabbing a new top with more holes in it.

In general if it's failing because of heat, it will just get worse over time as it indicates something is failing and most failing things get worse over time. Sometimes they are easy to fix if you catch them right away and difficult to impossible if you wait, so choose wisely.

I've had Ulka pumps work for 15 years in Vibiemme machines, so the problem is other than heat.

It's either the thermistor [which if you don't make back to back to back shots, you can remove] or the controller. They fail eventually due to poor location in the original design.