Originally posted by RichardP
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I've tried descaling steam thermoblocks warm, cold and hot and pumping solution through, letting it sit, cycling it frequently, cycling it less frequently, none of the methods have ever been as effective as turning the thermoblock temp down and the pump rate up and running the machine normally, letting it pump solution through for 30 second increments then allowing it to rest for 5 minutes or so with the machine off. Repeating this as many times as required until the solution coming out of the system returns to a normal colour.
Regarding your claim of potential steam pump damage, the steam pump has a relief valve fitted at it's outlet to resolve this exact type of problem. When the steam knob is shut completely, the excess steam pressure in the system vents out of the relief valve to the tray. If often makes a strange squeaking sound.
None of this steam gets to the internal parts of the steam pump. It does affect the rubber o-ring at the tip of the pump fitting though, over time it goes hard and leaks and is a primary cause of steam pump failures.
Perhaps you were referring to the Ulka pumps used in the EM6900, they experienced failures due to not having a relief valve fitted. The workaround was to file a slot on the steam tap pin which allowed the excess steam to vent through the steam tip. Not a great fix but it was effective and really the only option they had other than a system redesign (enter the 6910).

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