Vaillant Ecotec 937 plus - Flu fan constantly on, LCD dead, No heating or hot water - Common fault or not?

eveares

eveares

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Had a short power cut earlier and when the power came back on, it looks like my Vaillant Ecotec 937 plus boiler died.

My educated guess is either when the power went out or when the power came back on, the PCB on my boiler died, as now it is completely unresponsive (LCD dead, no heating or hot water) with the exception the flu fan is going full pelt. If not for the flu fan, I would think the boiler had no power.

Got a engineer coming out either today or tomorrow to fix it, but I just want to know for those that service and work on boilers generally, is this a common fault you see?

Boilers these days may be far more efficient and sophisticated, but the situation makes me think of my grandmothers old boiler that she had from the early 90's to the day she passed away, it was a very old wall mounted Glow Worm boiler that had a 24/7 pilot light and the only electrical part afaik was the gas valve to the main burner - don't recall it ever breaking down.

Regards: Elliott.
 
If the pcb died, I doubt the fan would be running. Maybe turn off at the spur, leave it 10 minutes and turn back on.
 
CBW said:
If the pcb died, I doubt the fan would be running. Maybe turn off at the spur, leave it 10 minutes and turn back on.
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Tried that already. When turning the switched FCU back on, the flu fan instantly starts straight away at full speed and stays like that, LCD does not light up and I do not hear any of the other components like the diverter valve move like I usually do when turning the boiler on.

This is just me guessing, but I wonder if the flu fan at full speed is a safety feature that should the main board die and the gas valve also happen to be open in the unlikely event, it runs to extract any flu gases outside. (Even though the combustion section is sealed and takes it's clean air from outside anyway AFAIK.)
 
ianmcd said:
Why was there a power cut ? if supplier cut the power they will pay to have the boiler fixed
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Don't know, it was a unplanned power cut according to the text message I got from UKPN. I am semi rural, so get a few short power cuts a year.

My consumer unit is from the era before house wide surge suppression was common place and thus I am wondering if I had a surge protection device installed, whether it would have made any difference to whatever killed my boiler.
 
eveares said:
Don't know, it was a unplanned power cut according to the text message I got from UKPN. I am semi rural, so get a few short power cuts a year.

My consumer unit is from the era before house wide surge suppression was common place and thus I am wondering if I had a surge protection device installed, whether it would have made any difference to whatever killed my boiler.
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The way modern boilers work, once the boiler stops a demand eithr the pump or the fan will over run to cool the heat exchanger, sounds like the power went off as the heat exchanger was still hot so the fan is running to try and cool it, you might have an OHeat stat that needs re-setting, not sure with your boiler but @ScottishGasMan will know , I have tagged him for you so he will see your request for advice, if the power out had damaged the PCB get in touch with your supplier thay are liable to sort it out
 
ianmcd said:
you might have an OHeat stat that needs re-setting, not sure with your boiler but @ScottishGasMan will know , I have tagged him for you so he will see your request for advice, if the power out had damaged the PCB get in touch with your supplier thay are liable to sort it out
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Hi Ian, these iirc only have a non resettable or non replaceable thermal fuse/cut off resulting in an F76 fault. Although I believe some of our engineers have replaced them as they're a bayonet type.
 
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muggles has it in one.


937 has 230V fan feed and low voltage control feed. The 230V is permanant and the fan will run constant if the low voltage feed is removed.

Assuming the boiler is around 10 years old then if the PCB has failed, turning the power off and back on will cause the fault to show, i.e capacators can hold a charge and continue to run even after they sort of die, but cut the power and reinstate it and they wont be able to come back online.

had it been a 938 (newer models) then at the oldest it could be is 8 year old, I'd then be more suspect that a surge has possibly taken the board out.

Either way, make sure the power is turned off for the time being or you'll burn the fan out and their not cheap.
 
Update, it was the main PCB, with that replaced, all is now all ok again.

Power cut the other day was only for a few minutes, but I knew something was wrong when the LCD screen had no back light or anything displayed on it. Error codes are utterly useless when the LCD is not lit up.

I am aware about pump and fan over runs on modern boilers to cool them down, however with the boiler switched off over night at the switched FCU feeding the boiler, the problem was still present in the morning.
 
Update 2: Discovered now that the heating was constantly on after the engineers had left, despite the thermostat not calling for heat.

TLDR, After a bit of investigation, I discovered the engineers had left the jumper link in place on the new PCB for the 24V thermostat option ("24V RT" terminal).

Removed said 24v jumper link and all is once fine again, with the annoying exception that the new PCB seems to have a higher minimum temperature for the DHW when comfort mode is enabled. I had it at 44c with comfort mode on before, now min temp with comfort mode is 50c.

Don't see anything to change this minimum DHW behaviour when comfort mode is enabled, tried turning "Legionella protection" off in diagnostic menu (always had Legionella protection turned off on old pcb), but made no difference.
 
Please be careful as from a safety point of view it should really only be a GSR that's inside the case, needed to get to the PCB. If I remember rightly the 937 is a room sealed case which means that unless the correct equipment is available and a qualified resource is able to test the boiler properly, then there is a risk that the seal could be compromised or not fitted properly and that could potentially put the people in the home at risk.
 
My understanding has all ways been (whether correct or incorrect) is that unless you are working on or opening components that involve gas or combustion, then you don’t need to be gas safe certified.

At no point have I ever opened the combustion chamber (which I guess may need a new seal if one did) or worked on the parts involving gas or combustion.


It was me also who removed the original Vaillant VRC 470 thermostat reciver and wired in my Hive thermostat to the PCB about 6 or 7 years ago.

Of course I am not advising people work on their own boilers, I’m just sharing my story.
 
eveares said:
My understanding has all ways been (whether correct or incorrect) is that unless you are working on or opening components that involve gas or combustion, then you don’t need to be gas safe certified.

At no point have I ever opened the combustion chamber (which I guess may need a new seal if one did) or worked on the parts involving gas or combustion.


It was me also who removed the original Vaillant VRC 470 thermostat reciver and wired in my Hive thermostat to the PCB about 6 or 7 years ago.

Of course I am not advising people work on their own boilers, I’m just sharing my story.
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The white front cover of the boiler firms the safety room seal and should only be removed & refitted by a Gas Safe Registered engineer. As to why you'd replace the VR470 with something that will make the boiler less efficient, well I guess that's something only you can answer
 
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