I'm going to throw my two cents in on this:
We two had an echo charger that wasn't working. It wasn't charging the coach batteries. The house batteries were at 13+v and the chassis batteries were down to 8v when I found them after just a few nights storage. We had just gotten the coach a week earlier and the whole electrical box was covered in dust. I grabbed my jumpper cables and charged the chassis batteries back up to full using my car alternator.
Using a woodshop hand broom and a shop vac in reverse, I was able to blow out most of the dust from the electrical panel that is mounted to the top of the battey compartment. The Echo Charger being one of the components up there was "caked" with dust in it's cooling fins.
With both the house batteries testing nearly the same voltage as each other, 13.2v and 12.4v, we shored the truck and put it back in storage. I went back to check on it a couple of days later.
Both the coach and chasis batteries were showing 14+ volts and both have maintained charge for the last couple of months. Now before you start thinking I must have jostled a wire with the brush, let me tell you every wire was securely fastened and every termination was tightly secured. No wires were jostled, but two things had changed: dust had been blown out and removed from the echo charger heatsink fins which may have caused the echo charger to overheat, and both banks of batteries were brought up to within 3 volts of each other.
If you look at your echo charger manual you will see a graft with a curved line that shows the charge response characteristics of the echo charger. The charger is designed (and implemented) to charge the chassis batteries from the house batteries only if the house batteries are fully charged AND when both banks are within 3 volts of one another.
So the echo charger may appear not to be working if one bank is 14.0v and the other bank is reading 10.9 volts or below.
This little echo charger came back to life when conditions were normal and has been working flawlessly ever since. So before you go replacing it, make sure both sets of batteries have ALL good cells, and are charged within 3 volts of the other bank when measured. But just remember, if one bank of batteries has just one or more dead cells, the voltage will drop below that 3 volt threshold and the echo charge will stop working as it was intended to.
Good luck!