Viessmann Vitodens WB1B Fd fault

[Agile]

Why do you think the boiler could not be at 115 C ?

I mentioned the temp sensor earlier today!

There are two problems, the sensor has to correctly report the temperature to the PCB, then the PCB has to instruct the components to run the boiler correctly.

There is a lot more than meets the eye to fault diagnosis when the problem is not very obvious.

Tony

 

[Phill Peck]

pump is not switching on,

This could be relevant!

Is the pump wired back to the boiler?

Bg will have fitted a 15-60 alpha 2 what setting is it on?

When it does work does everything get hot?

What area are u in?

 

[LL]

- Why do you think the boiler could not be at 115 C ?

Because this is when the boiler has been off for 5-6 hours approx and lots of ambient coldish air on ground floor

- I mentioned the temp sensor earlier today!

Thank you, I raised this suggestion to the engineers. This was a helpful suggestion and much appreciated

- Is the pump wired back to the boiler?

Yes
The last engineer suggested there is an overrun and he changed the bypass valve setup to enable more flow to cool the boiler effectively

- Bg will have fitted a 15-60 alpha 2 what setting is it on?

Not fitted by BG but same model. It is on the far left with power level 3. I did look at the manual and suggested another option but after having a call with Grundfos and with BG engineer there, this power option is the most powerful and will work albeit use a bit more power

- When it does work does everything get hot?

When the boiler, pump etc are all working then there are no signs of anything being wrong.. it will work for a day or a few days fine then start to play up again. Temperature regulates as expected, pump is running not too hot. The fault is intermittent.

- What area are u in?

North London


Thanks all for your time for input and response

[/i]

 

[Agile]

Do I take it that the temperature sensors have never been changed?

They are about twice the price of any other makers sensors, but still relatively cheap and always a potential intermittent fault source.

Having said that, the symptoms do not seem to be what I would expect from a faulty sensor, but everything has to be considered and sometimes boilers dont react as expected to fault conditions.

Tony

 

[LL]

Nope, the 2 engineers from Viessmann never changed the temperature sensors. it is on my prod list to ask them to do!

To clarify how they work, for my understanding, are they within the boiler measuring the temp of the water in the heat exchanger(s)? So if they are beyond 100 deg C (correctly or due to fault) they may be sending a message back to the boiler's PCB to shut down for safety reasons?

Many thanks

 

[Phill Peck]

I think you (or an engineer) needs to know if the pump is getting power when demand is on.

You said the valve opens but pump didn't start?

Could be a faulty pump but only way to know is if it's getting power.
The power from the pump comes from the pcb.
I'm pretty sure the boiler will run the pump if it overheats.

Was it a 3 port or 2 2 port valves?
Has the capsitir been fitted in the boiler between SL-N if not the boiler could be picking up demand from a 3port (specifically Honeywell) even when closed and would eventually overheat even with bypass open.

 

[Agile]

The sensors only indicate the temperature. They dont send any messages!

The PCB interprets the situation and during any apparent overheat would be expected to turn off the gas and run the pump!

Tony

 

[LL]

Sorry I used the word message when I meant a signal to be specific that PCB would interpret...

2 x 2 port valves. One is honeywell and not sure of the other brand from memory. One has been recently changed.

I can hear them opening and shutting on demand when I set boost/scheduled demand from the Hive controller. Whether they are sticking or another issue I'm not sure of.

Thank you all for your inputs - when the engineers next visit I will feed all these thoughts into them.

 

[LL]

Update for the benefit of the group:

We had Viessmann change another main board in the boiler and British Gas out again..

Viessmann noticed that the voltage input was too high at 256v.. this rose to 257.5v when BG were out..

It turned out that we have been having excessive voltage incoming to the property and the local area now for a while (unbeknown to us) and this has been frying the sensitive main board in the boiler (or at very least causing it to behave erratically).

The Viessmann engineer fitted a second capacitor to try to reduce the impact of any power spiking and I called UK power networks who investigated and found that our area were indeed receiving excessive voltage outside of normal tolerance. It is an issue that has been running for some time now apparently...

They have completed works this weekend and the issue appears (fingers crossed) resolved....!

 

[Agile]

There is a potential wide tolerance in the supply voltages from the mains.

Any sensible PCB design should be able to run with way in excess of +/- 10% of the nominal 240v mains supply.

 

[LL]

I was told that the standard is 230v minus 6% plus 10% typical tolerance. As we were outside of this range UK power networks investigated. When going above that sensitive resistors etc can begin to fail if not designed to cope with higher voltages.

I'm now hoping everything will be ok!