Need some help with oil burner not heating 1/2 the house...

Greetings ~
I have a Weil-McLein Gold oil burner and a forced hot water system feeling 7 radiators in a 2 story colonial.
At the end of last year sthe radiators in question started acting up, and the start of this year is no different.
So after bleeding all the radiators, having a tune-up with the tech telling me everything is functioning alright, I start to get aggravated. Some are blazing hot, others are just luke warm.
So today I check the burner itself at the pipes leading to the radiators...And I notice that the lower pipe off the burner is not getting as hot as the top pipe. Top and bottom pipe each lead to 1/2 the radiators in the house.
The bottom pipe has two valves, a big red one in line and a small blue one that appears to be a run off valve as there is an opeing attached to it.
The Red valve is twisted hard right, tightened - since I figure it can't hurt, I go the other way, loosening it to the left...Now the heat is better, but not blazing.
Now here is my question - could something this simple be the fix, and if so, why did the tech tighten it in the 1st place???
Bluesman
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You said lower pipe and top pipe, do you mean the pipes off the boiler, well one is cold return one is hot supply and of course both valves should never be closed. Does your recirculator pump run. Is your system filled, to what lb. Did you bleed radiators, are radiator valves open
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I think the big red one you describe, is a flowcheck, which prevents water from being siphoned from one zone to another. you'd need to be more clear about the controls on the system, such as zone valves and circulators to determine what could be causing this

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