A 2 year old (just out of warranty!) boiler has been throwing E125 since the day (literally) my Mother moved into her newly-built house. The fault has been raised with her Home builder who have called in Potterton engineers three times now as well as numerous visits by their own snaggers.
Over this time the whole System has been checked, drained, and a new controller PCB and CH flow NTC fitted. But it still throws E125 every couple of weeks or so. Reset brings it back. Now they want money for further callouts and that's plain ridiculous given that they've never been able to diagnose the problem which has been known about since day one.
So I'm studying the issue myself. I started with a description of E125: "Circulation Fault (Primary Circuit)". The details I find in the service manual are:
This suggests the controller is going on the flow NTC temperature reading and the internal timing alone. So not other sensor would seem to be involved. If I understand it correctly then, case "i) failure to rise by 1° in 15 seconds" would reflect a total stoppage of flow, e.g. failed pump or possibly misplaced divertor. But I would think this would not be something that would show up as intermittent.
If it's "ii) excessive temperature" (damn them for not giving us a unique E code!) then it's some circumstance where the flow has diminished to an unacceptable. But given the pump and other components check out OK, what's left that could cause this?
Just to add... I searched these forums and found many similar online discussions about E125 but not one ended with "it turned out to be X" or "doing Y fixed it"
Over this time the whole System has been checked, drained, and a new controller PCB and CH flow NTC fitted. But it still throws E125 every couple of weeks or so. Reset brings it back. Now they want money for further callouts and that's plain ridiculous given that they've never been able to diagnose the problem which has been known about since day one.
So I'm studying the issue myself. I started with a description of E125: "Circulation Fault (Primary Circuit)". The details I find in the service manual are:
E125 is displayed in either of two situations:-
i) If within 15 seconds of the burner lighting the boiler
temperature has not changed by 1°.
ii) If within 10 minutes of the burner lighting the boiler
temperature twice exceeds the selected temperature by 30°.
In these instances poor primary circulation is indicated.
i) If within 15 seconds of the burner lighting the boiler
temperature has not changed by 1°.
ii) If within 10 minutes of the burner lighting the boiler
temperature twice exceeds the selected temperature by 30°.
In these instances poor primary circulation is indicated.
This suggests the controller is going on the flow NTC temperature reading and the internal timing alone. So not other sensor would seem to be involved. If I understand it correctly then, case "i) failure to rise by 1° in 15 seconds" would reflect a total stoppage of flow, e.g. failed pump or possibly misplaced divertor. But I would think this would not be something that would show up as intermittent.
If it's "ii) excessive temperature" (damn them for not giving us a unique E code!) then it's some circumstance where the flow has diminished to an unacceptable. But given the pump and other components check out OK, what's left that could cause this?
Just to add... I searched these forums and found many similar online discussions about E125 but not one ended with "it turned out to be X" or "doing Y fixed it"
Last edited:
