I don't know.
Blockage (or partial blockage would be a better term since you are getting some circulation) are related as the run rate would be reduced if there was any impediment to the flow.
Check the Halstead documentation/instructions. The placement of and need for the bypass was covered...
Symptoms are rather like those I describe in a problem I had with a Halstead boiler in answering someone else's query. Text is reproduced below. Please adjust for your context.
"I had this problem with a Halstead a while ago. This boiler had a low-capacity heat exchanger (this is design...
No doubt about the rip off!
I had this problem with a Halstead a while ago. This boiler had a low-capacity heat exchanger (this is design, not a fault) that required a good flow of water through it. Pumping the water round the whole central heating system was too slow for it; the water in the...
Your description in message of 2 February 12:35 suggests that you loosened the retaining nut holding the valve to the radiator or to the pipe feeding the radiator.
If this is so, then probably you have put more air into that radiator.
To bleed the radiator, look for a small SQUARE bolt head...