Propably the steam pipe is blocked from dry milk. You can use a thin steel wire insert it in the pipe from bottom. If you manage to open it a little bit and start having steam then by boiling water and leave the steam pipe imerse in it it will melt the remaining dirt and by open the stem valve then the dirt will spoot out. If not then the valve is blocked or broken.
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Propably the steam pipe is blocked from dry milk. You can use a thin steel wire insert it in the pipe from bottom. If you manage to open it a little bit and start having steam then by boiling water and leave the steam pipe imerse in it it will melt the remaining dirt and by open the stem valve then the dirt will spoot out. If not then the valve is blocked or broken.