Water lines by-passed, think it needs new core, how do you replace core?

Yes. It could be th water pump.

You mean the heater...core...that's inside your heater case under dash? Am I understanding right? I can help you troubleshoot that. A core is just a very small radiator-same principle. Water going through the fins of the htr core warms the fins, so a htr motor blowing air across the htr core will blow warmer air out the other end, into ducts for a nice, toasty cabin.
Here's the problem with heater cores (gosh, I hope I"m not in outer space): Once the core gets plugged with corrosion, scale, or debris, and can't be gently flushed out forward or backward, then even a strong cleaning or treatment by a radiator shop is an iffy proposition. The core may lose efficiency in passing heat, and worse, is more vulnerable to leaking. So just buy a new one. No strong chemical fixes.
O.K. with a warm engine feel both heater lines where they enter the firewall. A htr core disipates only a small amount of heat. So your inlet line and your outlet line should both be equally hot, only a small amount of difference you might feel, like hot-Ouch.to hot-pretty dam warm. If one is significantly cooler than the other, there is a circulation problem-either clogged or an air pocket prevents circulation. Older cars had a mechanical valve in the line. I don't think anyone uses them in newer cars. You can check circulation by pulling off the outlet line near or around the car's water pump, or wherever convenient. Car needs to be running, so take it off first, hold your thumb over it, and have someone start the car. It wont be a strong stream, it should just be a steady stream. Since I don't know your specific problem, I'll just shut the () up.

Hello! There isn't a sensor that would disallow heated water to circulate through the heater core...If the temperature gauge rises to normal...And the upper radiator hose is hot along with the lower hose ...I can conclude water is circulating through the block...Question then becomes; Is it circulating through the heater core? And the answer to that is, I don't think so...With the heater control turned on high feel the outlet heater core hose (facing engine it's the one on the left) if it feels cold or not as hot as the inlet then one of two items are at fault...#1...The Plenum assembly, which the heater core sets in has an open vacuum line...#2...The heat control valve cable or the valve itself is not opening...See picture of valve below...It is on the firewall...Let me know if heat is passing through the heater core...If hot water isn't passing through the core and the valve is opening than the core itself is blocked...send a comment...Guru...Saailer

MOTORCRAFT Part # YG229...$20

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

ok is it water in your floor board or moisture if its water you heater core is leaking and needs to be replaced/ most of the time moisture on pass side floor is always a heater core prob/ if you need instructions on changing it let me know

I would try flushing heater core to see if it's plugged. I don't think it's waterpump, your rig would be overheating if it was. Leaking is most common waterpump failure.

You have a Valve on the pass side of the engine. It will have a small Vacuum line on top, and three water lines one of which goes to the heater core. This valve can get stopped up or the vacuum line falls off. Check that out. This valve lets the coolant flow into the core when open, or it by-passes back to the block.

You hot air comes from the water circulated through the heater core. It is like a miniture radiator with water flowing thru it constantly. So by opening the "Blend Door" you are permitting so much of this hot air to pass thru.

Seems like for some reason your heater core is plugged up. Just like a radiator can be. So water may be passing through your heater core but not passing through fully. Your heater core gets hot from water passing throught it from the engine. Then your doors open up, in proportion to how much air is permitted to pass over the heater core.

Suggest to remove the heater core and replace it. Seems the blend doors are working properly but again, if you have a non working heater core then no air can pass over the "Hot Core" for you to recieve hot air.

If you are not mechanically inclined, then go to a local parts store and you can buy a car manual, such as Chilton's or Hane's Car manuals, for your year and make to show you how to replace it. Then you can also have it for any other problems that may arise.

You may want to check your coolant level, low coolant will not circulate to heater core. You may have a plugged heater core, if you remove the 2 heater lines under the hood these lines i think a 3/4 and go directly into the firewall on the pass side.. take them off drain the coolant and flush it out by putting a water hose to one side and let it drain out of the other line. this is a cheap way to flush a heater core. good luck hope this helps

Your heater core has gone bad and needs to be replaced, If you go to Auto Zone you can pick up a new heater core and they will have the step by step instructions to doing the job yourself. If your lucky, may be the radiator hose to the heater core has failed at the cores pipes and it's only the hose that needs to be replaced but thinking not. You can get by pass the heater core for now so you can still get around till you pick up the new Heater core. Follow the two hose that goes to the fire wall and disconnect both of them from the pipe from the firewall, then with a pipe and two clamps, connect the two hose together and that's how you by pass the heater core. Good luck friend and hope this helps. 

FROM LUSTYKID:

Check to make sure your control lever is not disconnected. First

Second:
Check the motor controlling the heat cold/hot DOOR window. Sounds like its in the cold position, thus you are not getting the heat. The door needs to move and shut off the cold intake so that the air is passing through the heater core.

The third item is, although you flush the heater core, it can still be clogged up, in which case you will have to replace it. You probably flush the tanks of the heater core. Think of it as a miniature radiator. The tanks get clean, but unless the hot water passes from one end to the other through the vanes there is not heat, because the heater core is not getting hot.