Vaillant ecomax 824 2e

[kjharry]

I had a problem this morning with this boiler,when I arrived on site it was showing fault code f20 which is overheat.I checked the fault list in the menu and this has not happened before.The boiler lit after resetting it and ran ok,I checked the meter readings off the flow and return thermistors and the readings were correct,1.2k ohms at around 40 degrees.Everything warmed up through the building so I dont suspect the pump and dhw was fine too.The boiler came right up to max temp and shut off on the boiler stat,I let it cut in and out a few times and all was ok,or so I thought.When I turned the boiler off on the switch on the boiler fascia and turned it back on a minute later it went straight to f20 again,I reset it and it lit ok.I tried turning it off and on via the external programmer and it was fine every time,it only goes to f20 if I turn it off on the boiler switch on the fascia,on one occasion it showed f25 which is low system pressure,then went to f20,the system pressure is 1.5 bar.Has anyone else come across this scenario ?,I suspect the pcb and have one on order,but it would be nice to have some other thoughts,thanks.

 

[Agile]

Without further test information it might be difficult to diagnose whats wrong.

Whilst it might be the PCB that would be the last thing I would suspect.

Its best to check the NTCs with the boiler cold so that they are both at exactly the same temperature.

Sometimes on that style of Vaillant a sensor will seem to test OK but does not work until replaced, particularly after the boiler has been run dry.

Probably as a result of forced changes in the resistance curve.

Tony

 

[kjharry]

Thanks for that Tony,I will take both ntc's as well (its a 2 hour drive into mid Wales) and change those as well if you think they have been cooked by being run with low system pressure,but why would the the boiler go to f20 by being turned off and on at the fascia control ?,what other test information is relevant ?,thanks again.

 

[Agile]

I would want to do a full thermal survey to see if that identified any blockages or flow problems.

I assume these are the dry pocket NTCs? If so have you ensured that they are fully packed with thermal transfer paste?

Some earlier Vaillant boilers are reputed to have over sensitive protection software which has been upgraded in later models.

Tony

 

[gas4you]

If you turn off at mains you will not get any pump over run, so if hot will go to overheat.

Check auto bypass hasn't stuck shut and adjust d1 to 10mins.

 

[kjharry]

Thanks lads ,I will check all of theses things.When I turned the boiler off at the facia the temp was only showing around 55 degrees so I dont think it was lack of pump over-run though,and this is I believe one of the earlier models as it has the system pressure sensor near top-left in the boiler casing.