DHW Demand cuts out\reboots - Vaillent EcoTec Plus 831 - Help !!

[NemoNeil]

Hi fellow people, Help needed please

I have a Vaillent EcoTec Plus 831 which when hot water is turned on, the boiler starts firing up and immediately glitches or resets or reboots very quick and cuts off heating up the water.. and leaving the water on, the boiler retrys and does the same thing 2\3 times before burner stays constanly on and you get hot water.

theres no low pressure issue and seems to be fine.

there are No Error codes displayed. Reset to factory and still same.

this happens from cold start mostly i noticed when the boiler cools down.

Things that are new and recently changed in this boiler and less the 12months old are heat exchanger\divertor valve\ntc sensor\flow sensor\vesssel\gas valve

the only thing i can think of is the PCB?

posted a video:

as you can see start of the video i put the hot water tap on, nothing happens and temp starts to drop, when it reaches 32\31c you can hear it trying to fire up... when it does fire up full throttle, it cuts off, ... then starts to fire up again and this time round it stays on...
sometimes, when it cuts out, it kinda reboots it self, like scren goes off split sec and continues to try to fire up...

any ideas?

many thanks
Neil

 

[CountryFan]

Could be the pcb, but could be something else, like the flow sensor. Who’s replaced those parts and were they needed?

 

[NemoNeil]

Could be the pcb, but could be something else, like the flow sensor. Who’s replaced those parts and were they needed?

Flowsensor was replaced 6 months ago, not necessoraliy needed replacing, was recommended due to slight pressure issue assuming there was a block somewhere, but pressure is as normal now. no issues there. all parts were new

all was working until last week you dont get instant hot water, like now this morning, shower took 2 mins to come on and working fine after that, its only when it cools down, it starts to play up...

 

[Johntheo5]

Flowsensor was replaced 6 months ago, not necessoraliy needed replacing, was recommended due to slight pressure issue assuming there was a block somewhere, but pressure is as normal now. no issues there. all parts were new

all was working until last week you dont get instant hot water, like now this morning, shower took 2 mins to come on and working fine after that, its only when it cools down, it starts to play up...

Have you tried reducing the DHW temperature to say 50C, was the DHW temperatue sensor renewed?.

 

[NemoNeil]

Have you tried reducing the DHW temperature to say 50C, was the DHW temperatue sensor renewed?.

all sensors were new, I'll try reducing theDHW temp to 50c. I also have Comfort Mode on... let me test...

 

[Johntheo5]

If comfort mode is OFF, does the boiler fire up continuously from hot and cold?.

 

[NemoNeil]

If comfort mode is OFF, does the boiler fire up continuously from hot and cold?.

tried comfort mode off and setting down to 50c and still the same.... after a minute or 2 it start producing hot water....

i notice the lcd goes off and on very quickly when it start to fire up... also hearing a very slight humming noise from pcb.... not sure if thats normal... or a pcb fault?

 

[Johntheo5]

tried comfort mode off and setting down to 50c and still the same.... after a minute or 2 it start producing hot water....

i notice the lcd goes off and on very quickly when it start to fire up... also hearing a very slight humming noise from pcb.... not sure if thats normal... or a pcb fault?

Presume it then runs with a DHW temp of 50C?.

If its less than 1 year old then should be under warranty, if not, maybe ask Vaillant for a fixed charge to repair.

 

[NemoNeil]

Presume it then runs with a DHW temp of 50C?.

If its less than 1 year old then should be under warranty, if not, maybe ask Vaillant for a fixed charge to repair.

DHW does run at the set temp once its on...

Boiler is 10+ years old now....

 

[Johntheo5]

DHW does run at the set temp once its on...

Boiler is 10+ years old now....

The PHEX, diverter valve, flow sensor, DHW sensor, everything associated with DHW supply have recently been changed, so, possibly PCB, not much more left to change, does boiler fire up continuously from cold if CH is requested?.

 

[NemoNeil]

The PHEX, diverter valve, flow sensor, DHW sensor, everything associated with DHW supply have recently been changed, so, possibly PCB, not much more left to change, does boiler fire up continuously from cold if CH is requested?.

Same thing happens when CH is turned on, spases for few minutes before fireing up constanly... ordered a PCB, lets wait and see...

 

[Johntheo5]

Same thing happens when CH is turned on, spases for few minutes before fireing up constanly... ordered a PCB, lets wait and see...

This fault seems common to both CH&DHW so don't follow the logic of concentrating on replacing items associated with the DHW side, a bit surprising that no status, S codes, were displayed, no sure if they display automatically or have to be called up manually, they then disappear once the event corrects itself, it will be interesting to see if the PCB cures the problem.

 

[CountryFan]

This fault seems common to both CH&DHW so don't follow the logic of concentrating on replacing items associated with the DHW side, a bit surprising that no status, S codes, were displayed, no sure if they display automatically or have to be called up manually, they then disappear once the event corrects itself, it will be interesting to see if the PCB cures the problem.

On that model, to display status code, too 2 i-buttons must be pressed (usually twice, as first time lights display up)

 

[NemoNeil]

On that model, to display status code, too 2 i-buttons must be pressed (usually twice, as first time lights display up)

yeah i checked manually when i went to installer mode and display faults, no faul codes were displaying.. but if it clears it self after rebooting or something, then i have no way of knowing...

 

[NemoNeil]

Changed PCB, running smoothly for the past few days..

appreciate your help everyone