Aihe: Trumatic C 3402 (C343) probable overheating

Hello , sorry for post in English but I do not speak Finnish.

I've read all of the 21 pages (using translate) and didn't find similar issue .

So my Ducato's Pilote 2005 trumatic is working "ok" until ...

When started on winter heating (only flame icon in dial) , both fans start , 10 or so seconds later , gas valve , spark , second gas valve , minute or so later circulation fan increases speed and it's working as it should until reaching setpoint,  i presume second gas valve shuts off , circulation fan decreases speed , when needed second gas valve again kicks in, fan increased and so on .

All as it should for some time until I think it overheats , gas valve shut off , combustion fan off , and circulation fan goes to low ...later some time even lower speed almost no air whatsoever.

If I turn it off , wait a minute and whichever mode I select (water 60 , 40 , heating..) only circulation fan works on low speed.
First it blows hot air ...warm ...when almost cold air , gas valve kicks in again and then all normal .
This happens only if i don't use water from boiler...if we shower or wash dishes this doesn't happen only after prolonged time.
Like it overheats water and then goes to some lockout mode (wont heat) until water tank is "normal" temp again.
We own it for two years but never went to serious cold so probably didn't even know it has a problem .
Tonight ill try heating without water to see if this happens again.

Attached is temp diagram from my sensors. Green is inside temp , blue fridge temp , yellow outside temp . You can notice green line dipping that's when it's in that "cool down" mode and then heats again.

And all air wents are open I even added extension to heat the alcove and garage so there isn't blockage . Other gas appliances working ok .

Any advice ?
Thanks.
Goran

Sammuuko keltainen veden lämpötilan valo? Veikkaan, että anturi rikki.

Hi ,
Yes yellow light goes out in "about right time" as in when device cold its on for a while then off... even when selecting hot water if it's warm and yellow off (on 40) and i switch to 60 it's on again...so water between 40-60...if i try it later it won't light up even on 60 ...so i presumed water temp sensor was working ok . (All of that before overheat situation.. because when it locks out none of the commands are acknowledged)


Without water same thing but more time elapsed until overheat lockout.
First image slowly rising and than drop till I reseted it. because it turned on red light and went off completely which never happened with water.

This morning i measured all of the three temperature sensors and water temperature sensor didn't quite follow resistance/temperature relationship. So I disconnected it primarily to check if the boiler housing itself overheats or not with K-thermocouple and it holds at around 60c (without water) dial setting 6.
Pictures two and three.

For last two hours its working ok (nice power 1 ,power 2 cycling)  ,  I reduced desired setting to to see how it behaves with change (photo 4)

And for good measure I relocated electronics to adjacent wall...heat never goes good with electrinics ..wont hurt it.

If it turns out that it works ok, with water temp sensor dangling as is , is there already "known" substitution NTC or should I look for one with similar characteristics and preferably through hole mountable ?
Thank you.

I've searched online for truma sensor and found it a bit too expensive (75€) .
So I found matching NTC and bought 5 of them for 1€ . Placed it in cable end with eye, some epoxi glue and made me a diy through hole NTC.
Attached are photos of temp measurements. Water temperature is held at 65-70c when in heating mode . Real test once we go to sub zero temperatures .
Last picture green inside , blue outside temp.
Thank you for advice and time .

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