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 a valve was shutting off and going on suddenly and repetedly. I unplugged the connector from this (valve?) unit. Is this a valve? Do they go bad in such a way? Is this my problem and if I replace it will my heater problems be solved, or is there a decent chance that this has also screwed up the electronics behind the dash? Thanks for any help!