D
durhamplumber
I am not being funny...He has a constantly open rad..I still do not see what he would gain faffing on fitting an extra bypass.The pump is dumb and runs at a set speed....the pump will always operate at a point somewhere along its "pump curve" ie. the line showing the relationship between flowrate and available pump head (pressure).
As you close down the radiator valves the operating point on the pump curve moves leftwards and upwards with a reduction in flowrate and an increase in pressure across the system.
For example if you were foolish to shut all the valves (ignoring the boiler internal bypass) the pump would be "deadheaded" and with zero flowrate the head pressure would top out at around 5 or 6m depending on the pump fitted.
Having a towel radiator open would drop the operating point back down the curve a little and likewise the excessive pressure could be relieved by the opening of an automatic spring loaded bypass valve (adjusted accordingly).