As for the Gen x statement, eh maybe it was a low blow.

I would check with a local HVAC (Hydronic) wholesaler or installer to see if you can still obtain them {be prepared for them to cost almost the same {probably more when you factor in labour} as replacing the entire unit.As for using PEX, I'm not certain if the heat-rated PEX (used for in-floor hydronic heating which runs around 140F) can be used for a boiler and radiators (which typically run around 180F).  

Taxes appear low enough at about 45/mo on this property to not lose too much money.

A hot water heater isn't a big deal, but an heat pump is, when you hadn't planned on it! 

I also pay for heated water for all 4 units and that gas bill is around $50/m.

If anyone knows a lender that would be able to loan us enough to pay off our immediate needs which would be around $17000 with 1 low monthly payment for 12 months both my husband and I would be very appreciative.  

As investors we're always trying to get properties for as low as possible.  

What I am seeing is a lot more rehabs that are just carpet and paint and flippers leaving in old windows, heating systems which are on their last life. 

Interest rates are historically low.

I deal in SFH with rents 2-2.5x the "low" end rents for my area.