I might also suggest that the heater should be pressure flushed once a year and the shut-off valves in the engine compartment make this very easy to do since you can isolate (shut-off) the heater lines to the engine and install an extension hose to one line into a bucket then a garden hose to the other. The heater should be back flushed to remove the crap back through the supply line. I'll also mention a pair of plastic hose clamp pliars come in handy to keep the water from spraying all over the place when you disconnect the hoses from the valves!
Steve in VA
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