Federal Home Loan Bank of Boston Spokesman Mark Zelermeyer says a ratings downgrade is the reason the institution will no longer purchase mortgages insured by CMG Mortgage Insurance.

The primary mortgage insurer had been on a downward slide, ratings-wise, for months, including a July 29th ruling from Standard & Poor’s that gave the company a ‘BBB+’ rating.

Zelermeyer says the federal home loan bank of boston has a triple-A rating it would very much like to keep, and so made the decision to stop purchasing mortgages insured by CMG.

The bank will honor pre-existing agreements made on mortgages, and will stop buying CMG-backed loans as of October.

Furthermore, the bank has announced that such loans will no longer be eligible for sale under its mortgage partnership finance program, until further notice.

CMG is jointly owned by CUNA Mutual Insurance Society of PMI Mortgage Insurance Co.