As suggested, internal bypasses are never the best replacement for a properly installed external auto bypass (ABV).
The ABV performs 2 functions - min flow through the boiler to remove excess heat from the HEX when all valves close and min flow through the boiler to stop the pump pushing against a closed head.
Ideally the ABV would be as far away from the boiler as poss/practical.
The ABV performs 2 functions - min flow through the boiler to remove excess heat from the HEX when all valves close and min flow through the boiler to stop the pump pushing against a closed head.
Ideally the ABV would be as far away from the boiler as poss/practical.