The heater on my e-class started acting erratically and making weird "glass tinkling" and groaning noises. I checked the supplemental pump and it is drawing 960 millivolts, so based on previous posts here by Larry Bible I assume it is ok. However, I noticed that the shorter metal vertical canister in back of this little pump (a servo valve?) was getting extremely hot and I could feel the coolant flow thru the connecting heater hose surging like the valve was shutting off and going on suddenly and repetedly. I unplugged the connector from this valve unit.

Is this valve the culprit and all I need do is replace it? Or, is it likely that the electronics behind the dash are bad and sending it bad signals? Thanks for any help!