An update on this query is that after turning the Grundfos pump speed to maximum, (it has always been one digit below) the system ran fine overnight.
Today I have increased the boiler temp from Mar 3 to Mark 4 as it is normally, and also increased the room stat from 21 to 23 degrees (as it normally is), and for the past hour, the system has run without overheating.
My own thoughts are that if it stays as it is (hope so), is that the pump was not working correctly and probably sticking, on the setting it was on and now that I have put to maximum, it is disipating the heat.
Anyone confirm that this is feasible?
A further update is that the system is still running, but I have found that when I reduced the pump speed 1 below maximum, there was an overheat.
Reduce one digit more and there is a different sound on the pump, so hpefully the matter is now resolved. I will get a new pump fitted and in the meantime, leave the pump on maximum.
Other than the obvious (the speed the water is pumped) what is the correct or best speed to set a pump to run at?
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