is the 1/2" pex to restrictive for my situation?

[Enosez]

Here's the quick set up.
Have a boiler in a garage that is about 130' away from the main boiler in the house. (tenants rent house).
The house boiler is oil and tenants routinely run out of oil. Boiler is old.
I ran a zone of 1/2" pex out to the boiler to basically keep it warm and in dire situations to keep house/pipes from freezing.
Problem is, the flow switch does not activate the boiler even though the circulator is pumping.
My thought is the long run plus the possible restrictiveness of the boiler is keeping flow to a minimum.
I tried it using the circulator on the boiler (two circulators and yes flow is correct) also and still cant get the flow switch to open?

I can see movement of water in the pex I guess not enough to open the flow switch.

Before I spend money on a roll of 3/4" pex, does anyone think it will help?

 

[Jadnashua]

Not sure how much heat you'd get on 130' of 1/2" pex after pumping it that far - you'd lose a lot of heat just in the transfer. But, most pumps have an end switch in them that you could probably hook up to activate the boiler.