Hi,
My combi-boiler has just given up heating the house and basically only delivers hot water. While in central heating mode it heats up and stops to prevent overheating of the internal section of system. No fault or error code are displayed.
Suspicion: 3-way changeover valve assy.
So I temporarily switched boiler to hot water only. So finally I found some time to look under the hood:
I have suspected the stepper motor that controls the three way valve to be faulty. I pulled it off and measured it but it seems OK. Not sure if the valve itself works as it should, it lacks a bit of feeling to it.
So I have re-assembled everything and on power-up it seems to do a system self-test where the stepper motor moves up and down and then rests permanently in the up position (DHW), telling me that it is working and so is the electronic driver circuit. (This does not happen when pressing the reset button, which seems to be a more low-level reset.)
Again, when heating demand is active the stepper motor does not move from the DHW position yet the boiler starts heating, therefore reaching the temp limit of the internal hot water system and then switches off. Odd that there is no error feedback to stop this from happening, as the controller should be aware of the valve position, right?
When I pull the stepper motor off and move the three way valve to ‘heating circuit’ manually, the radiators warm up immediately, so pump and all else is good. Checked all the sensors, they measure OK as well.
Has anybody got an idea what might prevent the valve motor to change over? I suspect it is the valve itself or the hot water draw switch (that has priority) but the valve does not move. (It doesn’t require major force that the stepper motor would be overloaded). It just does nothing and just sits there. I checked the HW draw switch a year ago and it worked fine.
Anybody go any ideas where else to look before I start draining?
Thanks!
Michael
(While I am registered here as “DIY” I am a professional electrical and electronics engineer with degree and worked on quite a few heating systems and boilers. However I do not know the secrets of this boiler beyond the manuals and appreciate a hint from a professional.)
My combi-boiler has just given up heating the house and basically only delivers hot water. While in central heating mode it heats up and stops to prevent overheating of the internal section of system. No fault or error code are displayed.
Suspicion: 3-way changeover valve assy.
So I temporarily switched boiler to hot water only. So finally I found some time to look under the hood:
I have suspected the stepper motor that controls the three way valve to be faulty. I pulled it off and measured it but it seems OK. Not sure if the valve itself works as it should, it lacks a bit of feeling to it.
So I have re-assembled everything and on power-up it seems to do a system self-test where the stepper motor moves up and down and then rests permanently in the up position (DHW), telling me that it is working and so is the electronic driver circuit. (This does not happen when pressing the reset button, which seems to be a more low-level reset.)
Again, when heating demand is active the stepper motor does not move from the DHW position yet the boiler starts heating, therefore reaching the temp limit of the internal hot water system and then switches off. Odd that there is no error feedback to stop this from happening, as the controller should be aware of the valve position, right?
When I pull the stepper motor off and move the three way valve to ‘heating circuit’ manually, the radiators warm up immediately, so pump and all else is good. Checked all the sensors, they measure OK as well.
Has anybody got an idea what might prevent the valve motor to change over? I suspect it is the valve itself or the hot water draw switch (that has priority) but the valve does not move. (It doesn’t require major force that the stepper motor would be overloaded). It just does nothing and just sits there. I checked the HW draw switch a year ago and it worked fine.
Anybody go any ideas where else to look before I start draining?
Thanks!
Michael
(While I am registered here as “DIY” I am a professional electrical and electronics engineer with degree and worked on quite a few heating systems and boilers. However I do not know the secrets of this boiler beyond the manuals and appreciate a hint from a professional.)
