You said you blew out the lines. By any chance did you change the valve postion at the winterization port? If the valve is closed, them pump will not be able to pull water from the fresh water tank.
However, that does not explain your issues when you are connected to city water.
You said you blew out the lines. Did you remove the fresh water filter before or after doing so?
If not, the filter will still hold some water. It is possible the filter and any water in the housing could have froze and did damage.
As 16ACE27 said.... the city water line comes in and goes to a T. One sode of the T goes towards the pump abd yhe other towards the freah water filter.
__________________
|