Vibiemme Domobar: keeps heating until steam comes from OPV

#1: Post by **mamxs** » June 1st, 2014, 7:46 am

Hi all,

I've been using a (somewhat older) Vibiemme Domobar for a few months now, but last week it stopped working because the heating element broke down. This caused the machine to blow my electrical fuses when trying turning it on.

So I cleaned the whole machine: grouphead, boiler, pump and tubing etc. Then I replaced the heating element and corresponding nylon ring, the thermostat, the pump hose to the boiler and all the flexible tubing. After these replacements it turned back on again nicely, but it doesn't seem to stop heating. After a while the OPV puts out more and more steam through the backflow tube to the reservoir and I am forced to shut down the machine.

So the things I think I ruled out by now:
- the pump
- the thermostat (replaced), I've turned the screw completely counter clockwards to set it to the lowest temperature
- the heating element (replaced)

Does anyone have an idea what I can do?

#2: Post by **Randy G.** » June 1st, 2014, 9:58 am

[deleted by author - wrong model]

#3: Post by **another_jim** » June 1st, 2014, 1:42 pm

I think this is about the single boiler machine (i.e. not a Super Domobar) with the vapor bulb thermostat.

If that is right, then most likely you hardwired the heaters, bypassing 1) the vapor bulb brew thermostat (or the surface steam thermostat), and 2) the safety thermostat, so that the boiler pressure is exceeding 9 bar or 175C.

It could also be that both the vapor bulb and the safety stat are messed up. In that case the heat should switch off if you go to steam mode.

June 1st, 2014, 4:14 pm

Thanks for the quick replies, this is indeed about the single boiler machine (and not the 'Super' machine).

Another_jim:
I don't know what the vapor bulb is or where to find it. The safety thermostat is held around the boiler using a large spring I suppose?

I've tried your suggestion about switching on the steam mode: the heating does not stop when I do so.

Video of the machine starting up (machine was still hot from last try so it took only a minute):
https://www.youtube.com/watch?v=KQzPllU ... e=youtu.be

Here are some pictures of the machine:

Whole machine:

Wiring on the left side:

Connections to the thermostat:

Connections to the heating element:

http://users.rcn.com/erics/ · #5: Post by **erics** » June 1st, 2014, 4:32 pm

I don't know what the vapor bulb is or where to find it.

See pic below.

The vapor bulb is in the thermowell at the arrow. The bulb contains an inert gas which expands with temperature and flexes a diaphragm at the end of the connecting line. It "looks" as though that line has been kinked.

Doing a Google search on "vapor bulb thermostat" would be a little educational.

June 1st, 2014, 5:24 pm

Thanks for the info, here are some pictures of the old and the new thermostat + vapor bulbs:

Overview shot with the old thermostat + vapor bulb outside of the machine:

Close-up shot of the vapor bulbs: new one on the left, old on the right:

#7: Post by **another_jim** » June 1st, 2014, 5:46 pm

If the machine doesn't turn of when you have it on steam; I suspect you've miswired the heater so there is no switch at all on it. Isomac is kind of famous for the rats nest wiring inside their machines, so they may have jumped the neutral wire off the terminal on the heater to wherever it goes next. If you sent that back to the hot terminal wen you replaced the heater, you are going to have all kinds of grief.

June 2nd, 2014, 4:19 pm

Because I can't find a wiring diagram on the internet, I've drawn a wiring diagram of how the machine is wired right now. This means I do not have an idea where the wrong connection is made, and hopefully this could help solving the apparent miswiring:

Larger version: http://i.cubeupload.com/D5SgK4.jpg

http://users.rcn.com/erics/ · #9: Post by **erics** » June 2nd, 2014, 4:49 pm

The wires which you have connected to terminal 2 on the thermostat should be connected to terminal 1. I ASSUME this is a Prodigy TR/86 thermostat and, if so, this thermostat opens the connection between P1 and 1 on a temperature increase.

#10: Post by **another_jim** » June 2nd, 2014, 5:14 pm

The circle intersecting the boiler appears to be the hi limit switch and steam thermostat combined; it must be remaining closed and needs to be replaced. This is not the only problem, but it is definitely one problem.

Aside from Eric's point about the tstat terminals, there is also this: if the steam switch is broken and permanently on, it will bypass the thermostat and turn in the heat.