Hi everyone I'm new to the site so thanks in advance for any help.
I recently got an old isomac espresso machine and have been taking it apart. I'm having two problems
1- when I first turn on the machine the auto fill function works and refills the boiler with no problems. However once it gets hot and builds some pressure it won't refill the boiler. My theory is either the solenoid valve is old/ grubby and gets stuck when it heats up. But this is only a guess.

2- it appears that grubby coffee water is somehow getting from the group head and backwashing into the boiler because I pulled a shot this afternoon and then afterwards used the tea tap and it came out with coffee coloured water. My assumption is that I probably just need new seals throughout the group head.
So far I have taken apart the group head and cleaned everything, descaled the whole machine until clean vinegar was coming out.
Thanks so much for any help!!!

1. you can remove the autofill probe wire and see if it starts filling (don't do it too long) The other thing to check is that the boiler is not over filled, and you are not drawing enough water to expose the probe tip. If it doesn't fill then see below. Be careful not to expose the heating element.

This is often a symptom of a failing autofill box...they work fine when cold, but once warmed up they don't refill the boiler. You can double-check this with a multimeter once the machine is warmed up. Draw water from the hot tap...150ml whilst checking the voltage across the solenoid terminals. The solenoid is energised when the boiler requires filling.

2. The ONLY way this can happen is if the HX tube in the boiler has a hole in it leading to the main part of the boiler. You can confirm this by pulling a shot against a blind filter and watching the steam pressure. If it starts rising a lot and/or blows the safety valve, you have a hole in the HX. This can only be fixed with a replacement boiler

It's more likely that you have not noticed the dirty water from the tea tap before, or the limescale sediment in the bottom of the boiler has been stirred up enough to show some colour in the water. Until you fix point 1. above, I would be wary of drawing too much water from that tap, until you have confirmed the heating element is being switched off when the probe tip is exposed (which should happen the moment you disconnect the autofill probe wire).

Good luck

Thanks so much for your answer it's really helpful. When you say autofill box is that referring to the solenoid valve or is it a separate part?
I might have a bigger problem in my boiler but I'll keep troubleshooting to confirm.
Thanks so much I'm new to these machines and it really helps to have someone give me a hand.

DaveC wrote:1. you can remove the autofill probe wire and see if it starts filling (don't do it too long) The other thing to check is that the boiler is not over filled, and you are not drawing enough water to expose the probe tip. If it doesn't fill then see below. Be careful not to expose the heating element.

Dave, can you explain how this auto fill probe wire is supposed to work?
If you remove, the pump starts running to fill boiler. Does this indicate a working probe? BTW, without connection does pump simply run continuously?
If you remove and pump doesn't run, does this mean autofill probe is broken?

Cheers,

xenobasso wrote:Dave, can you explain how this auto fill probe wire is supposed to work?

1.If you remove, the pump starts running to fill boiler. Does this indicate a working probe?
2. BTW, without connection does pump simply run continuously?
3. If you remove and pump doesn't run, does this mean autofill probe is broken?

Cheers,

1. Yes
2. Yes
3. No, there could be a fault in the Autofill Box/Brain, broken pump, or the probe is grounding using something other than the wire, or the wire is grounding before the autofill box. The probe is a bit of metal that make electrical contact with the water and sheathed in teflon to avoid earthing at the point it enters the boiler.

Appreciate the response Dave.
Confirmed my probe is OK and working correctly!
Removed, cleaned and re-installed with fresh teflon tape.
Cheers,