What temperature triggers cut out E125?

[MisterBoy]

My baxi duo tec Combi 40 HE was off this morning with error E125 which seems likely down to overheating?
It restarted ok and has been running fine today but I'm watching the display as I run a Bath and it's sitting about 88C (heating and hot water set to 75 and 58 respectively).

We have had issues with heat exchangers before but I can't remember what the cutoff temperature is or find this online. Possibly 90C?

The heating and hot water are both working fine which makes me doubt external circulation restrictions... We have bled radiators and there's one radiator always open.
We had the system powerflushed this year so it would be disappointing if an exchanger has got crudded up again but is there another probable cause?

 

[CBW]

Have a look at the following, it shows why you may get an E125.

 

[gas112]

Sure no one turned off an isolation valve instead of filling valve ?

 

[MisterBoy]

Sure no one turned off an isolation valve instead of filling valve ?

Nobody has touched it for weeks until today and like I say my heating and hot water is working fine before and after restarting it.

 

[MisterBoy]

Have a look at the following, it shows why you may get an E125.

That's interesting thanks.
So i) could mean it's not actually lit or would that be detected separately?

For ii) which is the selected temperature? Hot water or heating?

 

[gas112]

That's interesting thanks.
So i) could mean it's not actually lit or would that be detected separately?

For ii) which is the selected temperature? Hot water or heating?

if it never lit that would be e133 code

 

[CBW]

That's interesting thanks.
So i) could mean it's not actually lit or would that be detected separately?

For ii) which is the selected temperature? Hot water or heating?

No, the code is still to do with temperature.

 

[MisterBoy]

No, the code is still to do with temperature.

I was just wondering under what circumstances it would be lit but not warming?
In my case seeing temperatures close to 90 it sounds like option ii but was just curious