E04 fan failure reading on thermo screen, heater turns on then off no heat, no blower...

Since you said you replaced the fan, and flow valve. Did you re-install the pressure switch correctly? it will look something like attached image. This is more than likely the cause if you did not replace with the fan or reinstall correctly... or it might have been the cause in the first place...

blower failure. either the blower isn't producing enough pressure, or the air proving switch is faulty, or you have a blockage within the vent or air switch tubing, or if the blower isn't coming on you have a failed relay within the circ board

fan failure. either issue with air pressure switch, blower isnt producing enough pressure, or blockage within venting

should be the coolant fan thats in front of the raidiator

Maybe not! there is a limit switch that has opened not allowing power to pass and start the furnace. You will need to tale a Ohm meter and follow the wires thru any safety switch. In your case, it may be the thermo-disc near or over the burner box. Jump it out to test it. Now why is your blower not working (which could have been the reason why the thermo-disc opened)? Once you find which safety switch is open and you have jumped it out, take a jumper wire and jump between the R and G terminals on the circuit board. This should start your fan. If not, either the fan is stuck, the fan motor is bad or hopefully noy; the circuit board is bad.

This problem is most likely caused by a damaged vac tube or bad vac switch. Check those first. The hose/tube may have been damaged, especially if you have any mice running around. It's most likely the vacuum tube, the switch is not as likely to fail but it's wise to make sure both are serviceable.

check that the silicone tube that that goes from air pressure switch to the fan does not have any holes in it. Caused by rats.

troubleshot vaccum switch determined it was operational (Use Pentair's website for service instructions on the switch) Fan speed too slow due to worn out motor. Replacing blower assembly

REMEMBER: when checking the resistance ensure that all wiring is disconnected from testing points!

Remove the top cover of the washing machine, you'll see about a foot size aluminum casing of the heater itself. Using a multimeter set on resistance (ohms) check the resistance between two welded pins (heating element) The readings should be roughly fom 0 to 26 ohms. If there's no readings you'll need to replace heating element, othervise check the resistance of thermo-fuse wich is located between those two welded heater pins. one of the wires connects heating element and thermo-fuse directly. The readings should be around 0 ohms, if no reading just replace the thermo-fuse.

Lets end at this point for now, as replacements thermo fuse solves the problem in most cases.

Please update me about your success, If unfortunately it didn't helped, just say and we'll find the solution!

Good luck

Check to see if there is a short between the green wire and the red wire. Green is the fan control wire for AC. Sounds like some wires may be touching. How did the old t-stat get fried?