The OP is now realising that the pump is probably not the problem:-
"""I'm in two minds whether my pump is actually at fault or if it's something else playing up..
So I'll start from the begining.
Switch the boiler on and wait for it to cycle and turn off, as there's no demand for CH and warm water.
Now turn the warm water tap on and the boiler will fire up and supply warm water to the tap, which is all good.
However, when the tap is closed and no more warm water is needed from the boiler, it will not switch off, instead it will keep running with the burner on and overheat and pop the Temp safety switch!
The only way to prevent it from overheating is by keeping the warm water running forever or by manually switching the boiler off however, when the boiler is switched back on it is still stuck in that position (warm water) so it will automatically fire back up as soon as you turn it back on and will keep burning and eventually cut-out (2-3mins) after overheating...
If I want to keep the house warm with CH I dare not touch the warm water tap in the house! If I do, it will be stuck to supply the warm water even after the tap is closed, then eventually over heat and cut-out as above. It fails to flick over to CH if there is demand or timer set on for CH...
For the past two days we have been using cold water and boiling kettles."""
That seems to me toi be a typical symptom of a stuck DHW demand switch!
Tony Glazier
"""I'm in two minds whether my pump is actually at fault or if it's something else playing up..
So I'll start from the begining.
Switch the boiler on and wait for it to cycle and turn off, as there's no demand for CH and warm water.
Now turn the warm water tap on and the boiler will fire up and supply warm water to the tap, which is all good.
However, when the tap is closed and no more warm water is needed from the boiler, it will not switch off, instead it will keep running with the burner on and overheat and pop the Temp safety switch!
The only way to prevent it from overheating is by keeping the warm water running forever or by manually switching the boiler off however, when the boiler is switched back on it is still stuck in that position (warm water) so it will automatically fire back up as soon as you turn it back on and will keep burning and eventually cut-out (2-3mins) after overheating...
If I want to keep the house warm with CH I dare not touch the warm water tap in the house! If I do, it will be stuck to supply the warm water even after the tap is closed, then eventually over heat and cut-out as above. It fails to flick over to CH if there is demand or timer set on for CH...
For the past two days we have been using cold water and boiling kettles."""
That seems to me toi be a typical symptom of a stuck DHW demand switch!
Tony Glazier
