Restricted propane Flow

Old-Biscuit wrote:
That's why one needs to try different set ups........otherwise you just start throwing parts at it

I'm not disagreeing with you, you and I are in agreement, nor did I "just throw parts at it"...I did as I stated in the first response to the OP's question in this thread , I checked tanks and hosing first, swapped tanks around etc...when nothing worked, I next replaced the red regulator...when that didn't work, I replaced the selector switch/regulator...that fixed it.

I took steps, why would you suggest I didn't and that I "just threw parts at it"? That's the way I took your post.

My suggestion was literally identical to your's...

What Old Biscuit said, I;ve had it happen (Red Regulator is most lickly bad)
Bob

That's why one needs to try different set ups........otherwise you just start throwing parts at it

I was going by my own personal experience with what seems to me to be the exact same problem as the OP's, less than a year ago....I swapped tanks, checked hoses, and then next step, to me was to replace the regulator on the side that wasn't allowing furnace to stay lit. .I then did what Old Biscuit suggested, replaced the "red" regulator...didn't make any difference, in my case, still had the issue, but doesn't mean it won't solve your problem, was just my first "replacement" of components in my trouble shooting steps. But, .furnace wouldn't stay on...Next, and only component that I had not checked was the selector/regulator on the drivers side of my 5er...I replaced the assembly and it immediately resolved my problem..Thus the reason I posted my opinion..Guess it could be wrong, but sounds like identical problem and a possible solution to his problem...it worked for me.

RED regulator on off side cylinder is a single stage 30# regulator.........they have been an issue.
They reduce cylinder pressure down to 30# before feeding it across to main 2 stage regulator.

Pigtails have a excess flow check valve---ball bearing style that closes off if pressure on both sides of ball are not equal.
They have been an issue with gumming up and sticking close.

Main 2 stage regulator takes cylinder/high line pressure and reduces it to 0.4 psi (11" WC) to feed propane system.
There have been issues with them.

Which one is causing your problem.......
Hard to tell via internet.
You need to swap cylinders around, try different set ups to eliminate issue
OR throw parts at it.......RED regulator first.

I had the same problem with mine Pete, I have two 40 gallon propane tanks, you can switch sides just like yours, my selector switch/regulator is located on the drivers side(Left side) of the 5er, the other tank located on the curb side, (right side) also has a red regulator....When I turned the furnace on, using the left side propane tank, there wasn't enough pressure to keep it lit, though it would have enough to cook with, to run hot water heater and to run the refrigerator. I checked hoses for obstructions, found none..replaced the red regulator on the side that couldn't keep the furnace lit....it didn't help..SOOOO, I replaced the regulator on the other where you select what tank you want to use, and BINGO...problem solved :).....Ever since I replaced the combination selector valve/regulator on the drivers side of the 5er, either tank will now keep the furnace going. That was my experience...

A picture would help???