The manufacturer, in the case, has in in-line particle filter since particles can have an adverse effect on their ball & float water feed mechanism (others have a water solenoid with a screen)
Often after a new install, some plumbing putty can effect the ball & float water feeder. Old galvanized pipes in the home can do it as well.
I'd be willing to bet that 95% of Thermasol installations do not have their recommended in-line filter since particles are not always an issue.
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