Looks like an older apparatus got a new paint job.
First time poster, long time lurker.
Believe it or not it's actually the reincarnation of Engine 25 (formerly Engine 4 a number of years ago) with a new pump and the decades old Squirt removed. This truck was always red, along with Engine 16 these two trucks were the first ever ordered by the CFD with the current red/white paint scheme.
If you look closely at the picture, you will see a few distinguishing features that set this truck aside from other older spare apparatus. First of all the superior logo on the front bumper and the fact that this is an E-ONE chassis. These were first purchased in 1994, bust still painted yellow (Engine 29) and then again in 1997 (Former Engine 4/25 and Engine 16). You will also notice the white Meteor light in the front grill, again, a common E-ONE feature. Note that the lower warning lights are all halogen flashers, including the front grille flashers by the headlights, and the side flashers. Again, the only E-One chassis trucks with this feature would be in the 1994-1997 era, and the only one purchased in that time frame with a flat roof as opposed to the raised cab that is standard now was former Engine 25. It was decommissioned for a while but has resurfaced now as a spare apparatus.
Any older yellow trucks in the spare fleet would be 1994 or older, and they would all be on a Pierce chassis, which this truck is definitely not. That's how you can tell that this is not a re-paint, just a modification on a former piece of apparatus.
Hope that clears up the mystery!