I've got a Vibiemme double Domobar, the older model with the vibe pump

I keep the switch on 1 ( brew boiler only ) typically, and lately ever so often I wake up & go to make a coffee and when I lift the lever the pump starts running but no water comes out. If I let it continue to run the temp readout on the front of the machine drops dramatically for a few seconds ( from 105C down to as low as 75C ) and finally the brew pressure goes up and I start getting some water from the portafilter.

The pump's already been replaced so it's definitely not that (problem occurred with the old pump as well as the new one )

ideas?

Just a guess, but maybe the brew valve isn't closing completely, resulting in the thermosphyon failing. The initial "no flow" pumping is the refilling of the brew pathway. See Constant dripping from E61 grouphead and Understanding and Preventing Thermosyphon Stall.

Thanks Dan

I wonder is that information still applicable to the double-boiler machines that use the E61 or if it's specific to HX machines (ie, I have no idea if my machine even uses a thermosiphon.)

But if it is, it might just be a matter of replacing a gasket somewhere along the brew pathway, the machine's ~5 years old & I've only ever replaced the grouphead gasket. I clean it regularly (once a week or thereabouts) so unfortunately a bit of cafiza isn't going to help.

HX or not, an E61 group has a thermosyphon (otherwise the grouphead would be cold since it's not bolted to the boiler). Check under the grouphead exit after the machine has idled for awhile. There should not be water. If there is, replace the gaskets. It's been 5 years; it may be worth replacing them all using this Grouphead E-61 Rebuild Kit.

Cool, thanks a lot. It's probably safe to assume old gaskets are the real culprit. I'll rebuild & see how it goes

The lesson, step-by-step, on overhauling the E-61 is on my website
HERE: Overhauling and Lubricating the E-61 Group