My fair Venus (Isomac) has recently started putting on a rather strange behaviour. Pretty soon after turning on the machine there is a build-up of pressure inside the boiler and when purging there is a significant amount of steam forced through the group head.

Brewing tends to be more dramatic than before. It is not uncommon that the extraction starts seemingly fine while half way through there's this sudden change of temperament and the shot ends up bubbly and over extracted (although tasting rather burned).

Now the most annoying part of the problem occurs when I switch off the pump. Immediately there is a substantial release/drop in pressure and a 'vacuum' literally sucking (loudly) the puck dry. This morning when I released the portafilter from the group head there was an explosion of coffee grounds as the puck disintegrated - torn between the group head filter and the portafilter - leaving a mess of coffee grounds all over the spill tray (unusually dry grounds though).

Apart from some dripping water from the stem wand-connection while steaming I've had no problems with her before. She was de-scaled last week, and that did unfortunately not change the behaviour.

Is there an easy fix to this?

foolishrice wrote:...there is a build-up of pressure inside the boiler and when purging there is a significant amount of steam forced through the group head... and the shot ends up [...] tasting rather burned.

These symptoms point to a failing thermostat. Or scale buildup acting as an insulator; if so, the thermostat would read the temperature lower than it really is, resulting in higher boiler temperature.

foolishrice wrote:This morning when I released the portafilter from the group head there was an explosion of coffee grounds as the puck disintegrated...

Sounds like the famous portafilter sneeze because the 3-way valve is stuck shut. If you're lucky, a simple cleaning may free the solenoid's piston. If you're unlucky, its coil has failed or it's not being power properly due to a failed electrical connection (see 3-Way Valve Hows and Whys for details).

foolishrice wrote:Is there an easy fix to this?

You mean one that doesn't require the disclaimer below?

DISCLAIMER wrote:THE ABOVE IS FOR INFORMATIONAL PURPOSES ONLY. MAINTENANCE SHOULD ONLY BE CARRIED OUT BY QUALIFIED TECHNICIANS. SUCH MAINTENANCE REQUIRES MANIPULATING AND/OR BEING IN CLOSE PROXIMITY TO CONTROLS AND CONDUITS FOR ELECTRICITY, VERY HOT WATER, STEAM AND HIGH WATER PRESSURE. THE RISKS OF FAILING TO FOLLOW PROPER SAFETY GUIDELINES AND PROCEDURES INCLUDE SERIOUS INJURY OR DEATH AND THE DESTRUCTION OF PROPERTY BY FIRE AND OTHER CAUSES. THE AUTHOR ACCEPTS NO RESPONSIBILITY FOR ANY INJURIES OR LOSSES RESULTING FROM ANY ATTEMPT TO PERFORM REPAIRS, DIAGNOSIS, OR MAINTENANCE.

Probably not.

I'm sure a good service would go down a treat! I have my machines regularly serviced & encourage my students to do the same. I'd definitely recommend having a tech guy do it & if you speak to the right companies you can often buy service kits or have them put together a kit for you.

Kim xxx

Thank you.

Despite owning an actual blind filter basket, I have to admit that I've been dreadfully negligent in backflushing. Repeated backflushing did seem to improve her manners. She no longer sucks the puck dry/sneeze post-brewing.

I'm making yet another de-scale attempt with slightly higher concentration of descaler and a longer exposure time.

Since feeling suspicious about the performance of the pressure relief valve, I disassembled it and cleaned it thoroughly this morning. Thereby I managed to remove some lime deposits the descaler hadn't reached to. This does not however seem to have changed the symptoms of steam build-up before brewing. I suppose this further suggests that the brew thermostat is to blame?

Replacing the thermostat doesn't appear that difficult; if only I can get to it. It's pretty narrow and the components do sit quite tight.

I got in contact with an generic espresso machine company in Stockholm and they informed me that their hourly rate is 500 SEK excluding tax (equivalent to $ 96 or £ 59). And then there is the cost of transport and spare parts. Is it worthwhile?

I suppose getting a service kit can be more economical; if only I could order the parts online.

I'm just guessing BUT - I suspect you have three thermostats on that machine and, as Dan said, it sure does sound like the brew thermostat has failed closed. So why not post a pic of your machine's interior to help others help you?

In addition, why not remove the dispersion screen and soak all those parts in a cleaner such as Cafiza or similar?

Yes, that's right, there are three thermostats. A brew thermostat (100°C), one for steam (145°) and one safety thermostat which has to be reset if released...

I'm attaching a picture of the interiors. The photo was taken from an angle facing the front of the machine, slightly from the right...

The brew thermostat screws into the top of the boiler via an M4 thread. It is surprisingly easy to overtighten that thermostat and snap the connection. Even so, I would recommend you replace the brew thermostat. Apply a little thermal grease to the contact surface and screw the new one in BY HAND until it is fully seated. Now tighten with a wrench until "snug" - about 1/12 of a turn.

I loosened the thermostat, it wasn't as hard as I'd imagined.

After putting it back I took the temperature of the boiler (by placing a probe at the base of the thermostat). I got readings between 105 and 120 °C and the thermostat seemed to switch on at 105°C, as indicated by the light indicator (I recognize that my thermometer probably lags behind a bit). The steady state temperature was approx. 115°C; is this normal?

What else, other than a faulty thermostat, could cause the steam build-up?

It's a petty there aren't variable thermostats...

I think that that temperature range is too high for a Venus. Could be due to poor thermal contact between boiler and thermostat or a bad thermostat. Because it is easy and cheap, though, I would just replace the brew thermostat as a troubleshooting step.

Jim

Ok,

I could not see any thermal grease on either of the thermostats, not even traces there of. I'll definitely be getting some of that.

What about getting a thermostat rated for a temperature slightly below 100°C?

Markus