viessmann vitodens overshoots after replacing the board

prunoki

Hi,

I have a Viessmann Vitodens 200 with one heating circuit and a Vitotrol 300 in the living room. The system was installed 5 years ago and it has been working fine until a week ago, when all went haywire: system working fine for 20-30 minutes after powering and after that there were strong noises from the "ventillator" (if there is any), the burner did not fire up anymore and once I received an error code FE.

The guy who came to repair it was quite clueless then spent some time on the phone talking to Viessmann. He left and came back with a new electronic board, kinda like a motherboard for a PC. He put in the new one and for a while everything seemed ok (at least in the sense that I had heating). Then I realized that the system overshoots the target temperature. If I want 20C in the room I have to set 16C. When I set 17C, the heat pump and the burner was still on et 22C. The old board never did that, when I set 20C the temp varied between 20 and 21 degrees. Is this normal? Any ideas what might be causing this?

Regards,

Krisztian

the_donut

From service manual; FE code relates to burner code card being faulty. Settings got reset after replacement.

General settings, 9F. Default setting for heating curve is 1.4. For cast iron suggested is 0.7-1.2. I would try 0.9 for now and see if that helps. If temp overshoots, reduce value more. If undershoots, increase it. There may be other settings to adjust, but since issue is more pronounced in mild weather this is probably the issue.

the_donut

Also page 36 details adjusting heat curve for desired room temperature. This may require some tweaking as well.

prunoki

Thanks for the tip. There was -4 Celsius outside in the morning. What I do not get is that if the heater knows that the temp is already 22 and the desired temp is 17 why does it keep going? It is not an overshoot due to the water being too hot.

neilc

bad thermostat ?
or bad / wrong thermostat wires at the changed board ?

prunoki

The display on the heater shows the correct values, I thought that excluded a wiring problem.

neilc

forget what I wrote above if it does shut off eventually, (even if too hot),
it does shut off, correct?
this is just a matter of overshooting, correct?
then it's settings or other sensors

the_donut

Control unit has a lot of settings. One thought is circulator runs after call for heat end. Boiler shuts off on temp but residual heat in system radiates and overshoots target.

prunoki

Yes. I just made a small movie to show you what happens. You can see on the video that the burner is on, boiler temp is 50C, so the heating is on. When I go to the information panel you will see that the room temp is already 22, the "set room temp" is only 20. If I decreased the set room temp it would shut off.

https://photos.app.goo.gl/hRwdMPe9Qul3Hamv2

prunoki

No, the boiler does not shut off, it is not the "residual" heat in the radiators that causes the overshoot.

the_donut

Does it only shut off when adjust temperature or does it eventually shut off on its on?

Paul Pollets

the heating curve is responsible for the temps in the radiators or RFH. Adjust the curve downward to lower the overshoot. each .1 adjustment reduces (or increases) the temps by 3 degrees. leave the curve alone for 24 hrs to allow the computer to compensate. everytime you make a curve adjustment, the computer dumps its memory and starts recollecting data.

ubik

Hi @prunoki, 
I had exactly the same problem. FE error code, replaced main board (very expensive repair) and the heater always acted weirdly as you describe. I complained with the service company and Viessmann, but they were not able to diagnose the problem. After two years the main board is faulty again. I will never buy Viessmann again. Their electronic compnents are faulty and extremely expensive. 
Were you able to solve the overshooting problem?

sunlight33

Can you check coding level 2 address b0 and b5 and tell me their values?

GW

^^^^^^ this 

what is the model number? There’s several generations of the vitodens 200. You have B2HB? 

vvvvvvvv here is what you want

ubik

@nlight33, in my case B0:3 and B5:0, but believe me: I tried also changing those values and also other related values, but unfortunately what I (and probably also @prunoki) am experiencing is not just a bad setting. It is a faulty behaviour of the board.
@GW, my exact model is Vitodens 200W WB2C K 26kW ECP IT.

Moreover as I mentioned, after 2 years since the board was replaced (at my own expenses, it costed about 600€) it is acting weird again: now it thinks that it is equipped with a low loss header (my system does not have a low loss header, but address 52 is set to 1 and even if I try to set it back to 0 it returns back to 1). It also senses a 0°C temperature at the (missing) low loss header temperature sensor. This causes major malfunctions to the heater since it thinks that ice is coming out of its boiler ...
I already called Viessmann service (at my own expenses: 75€) and they diagnosed faulty board which needs to be replaced... again... after 2 years... at my own expenses... 600 € again!!!! They refused to replace it under warranty.
I said that I prefer to replace the whole heater and that I will never buy Viessmann again!
In the meantime I was able to find a workaround by attaching a 10k thermistor to the low loss header sensor connector (X3.4 and X3.5) and I placed the sensor in contact with the pipe exiting the heater, so that it senses at least a realistic temperature instead of 0°C. This allows me to have a functional heating while I arrange its replacement.
The conclusion is: I WILL NEVER BUY VIESSMANN again!

Paul Pollets

ubik, I would contact the national sales manager and tell him of your problems and concerns. I've had 2 bad boards in succession, but they were under warranty.

GW

OK I thought we were talking usa, maybe your model is slightly different, not sure.

ubik

Paul Pollets said:

ubik, I would contact the national sales manager and tell him of your problems and concerns. I've had 2 bad boards in succession, but they were under warranty.

Paul, this is one of the reasons why I am quite disappointed with Viessmann service. I already contacted the sales manager, but he never replies to my emails. When he answers my phone calls he says that he will check with the local service company and he will let me know, but then he never gets back to me.
I am thinking about contacting Viessmann in Germany to override also the Italian sales offices, but as I said I am disappointed and tired. Anyway thank you very much for your support and suggestions. 

Paul Pollets

Call 800-387-7373 and ask for Herald Prell, the director of Viessmann N. America. He'll return your call.

ubik

Hi, a quick update on my case: in March I was contacted by the viessmann authorized service company to replace the faulty main board again. I had to pay only for labor and not for the part.
After few weeks of normal behaviour it started overshoting again. A couple of weeks ago I called the service company again, they could see the overshooting and intermittent firing of the heater and checked all the parts. Then they contacted Viessmann and after a few hours of checks they suggested to perform a factory reset (not the normal reset, they did it using undocumented codes). The reset improved a little bit the behaviour, reducing the frequency and intensity of overshoots, but the heater is still overshooting and is not capable to properly modulate the flame to the desired temperature.

Alan (California Radiant) Forbes

Thanks for the update!

Has anyone suggested that the problem is because you don't have a low-loss header? That when the boiler fires, the flow through the boiler is not enough to carry all the heat being generated and it overshoots the mark.

Jamie Hall (I'm sure) will follow and elaborate.

Jamie Hall

I think -- based on nothing more than a little blue sky thought -- that @Alan (California Radiant) Forbes may have it. You have no low loss header. You have no low loss header temperature input to the controls. Now mind you I know nothing about how the Viessmann control algorithms are set up. However, if I were doing it, I'd have the return temperature sensor in the loop, and use the rate of change of that temperature in relation to the setpoint to downfire or shut off the boiler before it would overshoot. Without that input, all the poor thing knows is that it's either at the setpoint or not, so it fires until it hits the setpoint, then shuts off -- and, of course, overshoots.

sunlight33

You said you placed the LLH sensor in contact with the pipe exiting the heater, so what's the temperature of the pipe relative to the boiler temperature? Are they very close to each other?

Paul Pollets

I'd be installing the LLH and sensor before trying another board. The boiler can't provide over 7gpm without it.

ubik

Thank you for your comments, here are my considerations:
- the installer has designed the heating system without low loss header, and I am assuming that I don't need one
- The heater worked perfectly fine for 6 years, then it started overshooting for a still unknown reason, so I assume the problem is not in the wrong design or in the lack of a low loss header
- two Viessmann authorized service centers have tried to diagnose the problem, also guided by the Viessmann central tecnhical offices and they never mentioned that the problem is due to the lack of a low loss header
- I don't need more than 7gpm, just 13 lpm (about 3.5gpm)
- the problem is not if the flow rate but instead in the inability of the boiler to modulate
- The overshoots are not due to the inability of the flow through the boiler to carry all the heat being generated, because when I check the modulation percentage I can see that the boiler is pushing at 100% or around 80%. Since my heater has a 1:6 modulation ratio I would expect that it should reduce the modulation to about 17% (100% divided by 6) before giving up and stopping the flame. Again, in the past I could see that the heater was able to modulate down to 17%, now it simply doesn't and no one is able to diagnose what's wrong.

sunlight33

Previously I had an issue with my boiler (also a Viessmann 200) failing to modulate, it would heat itself to reach shutdown temperature. I fixed it by replacing the coding card and gas valve.

ubik

Thank you @sunlight33, I explicitly asked the service technician (both the previous and the current one) if the coding card or the gas valve could be the cause of the malfunctioning. In both cases they asked the central Viessmannn support and they said that it was not possible. Your experience is interesting. I found a Viessmann technical training document in which they suggest to replace the coding card and the gas valve together with the electronic board. It is however very strange that the diagnostic system does not report any fault to these components. In your case did you get some specific error code? How were you able to track the problem down to the gas valve and coding card?

sunlight33

No code for me. Long story short, I tracked the problem down to gas valve because I (and the contractor) replaced almost every other part of the boiler associated with ignition but the issue persisted. It's like going through a process of elimination, expensive yes. That's why later on I ended up buying and replacing the parts myself. Coding card was replaced early on, it was cheap and very easy to replace, the boiler worked for a while but didn't solve the issue. But YMMV.

ubik

@sunlight33, your description makes a lot of sense to me. The symptoms suggest me that some component of the lambda pro modulation control system is the culprit and the gas valve is one of the main candidates. Unfortunately the gas valve mounted in my heater is calibrated at the factory and cannot be recalibrated at home, as far as I know. I will discuss about your experience with the service technician.
Does anyone in this forum know if there is a diagnostic test which can be performed to check the gas valve correct functionality of the vitodens 200?