Vaillant Ecotec Plus 418 problem - will not start up

[tagb61]

If the boiler is showing S.30 with 240VAC on T4, odds on its a new PCB. Double check at D.8, 0 is no signal recognised from external controls, 1 signal recognised from external controls. Expect 0 in your case. Double check the wire to T4 is tight and test to the Neutral terminal or T5 on the PCB. A board replacement is not out of the way at 10+ years. They are susceptible to power supply rail issues the older they get with capacitors failing, so don’t feel too hard done by. Setting up and combustion checks with a FGA need to be carried out by a GasSafe engineer when fitting a new PCB.

Thanks. In case it's a faulty wire connection, I'm going to check that out the voltage on T4 is actually 240V with a meter, and try the link between T3-T4 to confirm the fault is still there. I'll probably go the replace pcb route.

 

[DP]

Thanks. In case it's a faulty wire connection, I'm going to check that out the voltage on T4 is actually 240V with a meter, and try the link between T3-T4 to confirm the fault is still there. I'll probably go the replace pcb route.

Once you replace the PCB, how are you going to carry out flue gas analysis

 

[tagb61]

That's the next challenge. The boiler needs a service anyway, hopefully that can be done as part of that.

 

[tagb61]

I have checked the voltage on Term 4 is 240VAC when there is a demand for heating, hot water. Checked connections on the terminal block are tight, and tried link between Term 3 and Term 4. The boiler status still reports S.30 no demand for heating. As suggested I double checked setting of D.8. It also reads 0. It seems the pcb must be at fault.

 

[DP]

I have checked the voltage on Term 4 is 240VAC when there is a demand for heating, hot water. Checked connections on the terminal block are tight, and tried link between Term 3 and Term 4. The boiler status still reports S.30 no demand for heating. As suggested I double checked setting of D.8. It also reads 0. It seems the pcb must be at fault.

While this is not going to help you, understating the cause can be comforting at times

Lot of PCBs, 240 volts, through network of components is offered as a low voltage to a 4 pin package. Within the package there is an LED that lights to application 240 volts at the said terminals. In close proximity is a light sensor that is looking for this light and acts as a switch to get things moving. Have in the past changed this part to get a PCB working

 

[tagb61]

While this is not going to help you, understating the cause can be comforting at times

Lot of PCBs, 240 volts, through network of components is offered as a low voltage to a 4 pin package. Within the package there is an LED that lights to application 240 volts at the said terminals. In close proximity is a light sensor that is looking for this light and acts as a switch to get things moving. Have in the past changed this part to get a PCB working

It is interesting to speculate on the cause for the pcb issue. The opto-isolator is a good suggestion for the failure point. As the board is pretty old, I've decided to change the it anyway as other parts may be close to failing too.

 

[DP]

It is interesting to speculate on the cause for the pcb issue. The opto-isolator is a good suggestion for the failure point. As the board is pretty old, I've decided to change the it anyway as other parts may be close to failing too.

Would you know what to look for or how to test it? Replacing the PCB as the Vaillant guru - The 831 Bunny -suggested will entail carrying out flue gas analysis

Area we are talking about is beyond the boundaries enclosed by day to day boiler repairs

 

[tagb61]

I've arranged for a gas safe engineer to change the pcb and carry out any safety checks needed.
As it happens the installation manual for the boiler covers pcb replacement, and any setup/checks needed. It was straightforward and didn't require a FGA that I could see, but to be sure I am going the gas safe engineer route.

However as a professional electronics hardware designer and having worked on many board designs I am curious about the electronics involved in the failure

 

[DP]

I've arranged for a gas safe engineer to change the pcb and carry out any safety checks needed.
As it happens the installation manual for the boiler covers pcb replacement, and any setup/checks needed. It was straightforward and didn't require a FGA that I could see, but to be sure I am going the gas safe engineer route.

However as a professional electronics hardware designer and having worked on many board designs I am curious about the electronics involved in the failure

Trace the 3/4 termination to point of switching will get you there.
If you are a hardware designer then it should be a walk in the park
I suppose no point in flagging the high DC voltage on that PCB which you will already have realised

 

[Agile]

But he could look at the opto isolator if it uses one to isolate the switched live from the boiler circuitry.

But he may find a lot of the circuitry rather before his time.

 

[tagb61]

I hope not, I designed my first boards in the 1980's
Anyway a gas safe engineer has replaced the pcb, and all is good. He carried out the required safety checks including the FGA. Nice and toasty now.

 

[Agile]

Well I am glad that we correctly advised that it seemed to be the PCB

But that PCB is all analogue with no CPU or memory or look up tables.

Unlike current PCBS which operate as small computers and often get computer like silly faults and can be very sensitive to switch on sequences. And digitise sensor outputs and check the readings against look up tables to ensure they are within design parameters.

All is well that ends well.