Looking for some general information regarding Back Office or ACH Conversion of HELOC checks:
Under current NACHA rules, a HELOC check cannot be converted to an ACH payment as it is not a demand account. However, based on typical MICR line encoding, there is generally no unique encoding to differentiate a HELOC check from a personal check.
So, how many HELOC checks are in-advertently converted to ACH format for presentment and payment? And, is there a move or desire within the industry to try and prevent this conversion?

NACHA rules don't limit check conversions to checks on demand accounts. Money Market Deposit Account (MMDA) checks are eligible, for example. However, the BOC rules do state that HELOC checks are not eligible. As Buzz notes, if the HELOC checks are not in "business check" format, with encoding in the auxiliary on-us field of the MICR line (normally where business check serial numbers are encoded), there is often no way for the payee business to know of their special status.