Vaillant F22 random errors?

[Agile]

I attended this boiler last week and cleaned the plate HE as it was seriously blocked.

DHW is now working fine and the system pressure is 1.5 bar. The pump is OK and the impeller clean.

However the client reports its giving occasional F22 errors.

If I recall correctly this error is deduced by temperature sensors on flow and return of the primary HE being outside the allowable range preset.

I have previously found this is apparently caused by the two NTCs testing for resistance OK but presumably not having adequately matched curves. This often occurs following dry firing. Replacing them with new sensors usually solves the problem.

Does anyone have experience of other causes of random F22 errors ?

Do I correctly remember that these are dry pocket? If so then does lack of heat transfer paste ever cause this?

Tony

 

[corgigazza]

On some of the early vaillants the boards do go to f22 (non condensing thermocompact) quite often, when on vaillant coarse asked about this and was told the software on these boards was incorrect between the flow & return temperatures and subsequent boards increased the time / temperture rise allowances,
Also was told if system boiler was fitted and on hw return, no gate valve was fitted this increased the return temp to quick causing f22.

Have fitted new 3 boards so far and this cured that fault but also check pump and for airlock etc.

 

[Gasguru]

Always replaced the NTC's - dry pocket easy fit.

 

[pannierstan]

Yep me too

 

[Agile]

Is that a 2:1 vote for replacing the sensors ( first ) ? At least its cheapest!

My problem is partly that the ( Asian ) customer of course says its only happened since I cleaned the plate and will probably say that she thinks it should be fixed free!

I will leave it another day and see if the frequency slows down. It seems to be quite a common problem with these trips.

Has anyone tried the effect of just adding heat transfer paste, perhaps just to one sensor? ( Which one? )

Tony