In my rented townhouse I had an HRV system. Had never had experience with one before. I changed the furnace filters regularly, but didn't realize I should be cleaning the HRV filters at the same time. So I didn't clean the filters for about 4 years. The landlord had never mentioned it, and when I later told him about it he said he had no idea that cleaning the HRV filters was required.
2 years ago in very cold weather my gas furnace started to flame out, and the house would get very cold. I was able to solve it by tuning off the HRV unit.
Then I researched it and found out about the necessity of cleaning the HRV filters regularly. When I opened the HRV unit I found the intake filter totally clogged with dirt and debris from outside. The output filter was dirty, but not nearly as bad. In my HRV unit they were washable foam filters, so it was simple wash, let dry, and put them back in the intake and output sides of the core. No problems since then...