Delonghi Magnifica ESAM 4200 steam problem

[JJcoffeeEnjoyer]

Heya folks, I'm having problems with the steamer on my all on one machine, hoping someone can help.

Details:

• It's a single boiler machine
•  It produces coffee fine
• It produces hot water fine
• It's been regularly descaled

Problem description:

• When I press the steam button, then wait for the light to go solid, I turn the steam knob
• The machine produces only tiny spurts of steam, barely works at all.
• Also the pump only moves very slowly - I hear "put... put ... put" instead of the continuous vibration/pumping I get when I make coffee
• HOWEVER if I turn the steam button off, then open the tap, I get about 10 seconds of steam before I get hot water again.

I don't know what this means. I think it might mean either the safety overpressure valve is gone, or there's a problem with the thermosensor on the boiler/generator, but I don't want to replace the wrong bit!
The machine is clearly producing some pressure though, as I do get steam when I turn steam mode OFF, and the coffee is still good enough.

I don't think it's the steam valve on the front, as that just opens the spout and tells the pump to go, right? I don't see how this outlet valve could impact steam generation.

Any advice gratefully received!
Thanks,
Jasper

 

[MarcBeck]

I would look at the overfill sensor. My guess is it's allowing too much water into the boiler and consequently there isn't enough room in the boiler for steam as it's filled the boiler too much/high. Especially since you said the pump is moving slow. It's probably trying to pump water into an already totally full boiler.