Vaillant boiler showing F64?

I have a Valliant ecotec plus which originally came up with various F. codes so I changed the control panel pcb and it settled down for a few weeks. It then started coming up with F.64 quite regularly, so I changed both of the NTC sensors and again it settled, but now when we get up in the morning it has cut out with F.64..Does anyone have any thoughts?

Thistle1
February 2017

Ours has just done this and died. I did say this morning I could smell gas when I passed the boiler cupboard and then tonight it's gone off. Waiting for the diagnosis. Nothing in the handbook to help with this code.

basilizzy
September 2012

faulty pcb

T Khan
October 2010

Looks like mine has been repaired. Firstly it is a model 837 ecotec. There are two ratio's the engineers check for a gas valve in the boiler, apparantly it is normal the lower reading always follows the upper reading and it is not normal to check the lower ratio if the upper one is fine. The engineer spotted the flame was faltering and tested the lower ratio for this valve and found it to be wrong. This would have caused the flame to become unstable and go out, the boiler would think it was an Ntsc flow sensor failure but there is nothing wrong with the sensor.
The valve has been changed and all now appears to be well. Massive thanks to the Vaillant engineer who would not let himself be beaten by this.
Hope this info helps someone

mike787
February 2010

Well, mine is still failing, it is now doing it 3 to 4 times a night. British Gas have acknowledged they have no idea, they have also replaced the wiring harness and it is still happening. I have now been waiting almost a week for Vaillant to make contact under the authority of British Gas to try and get this sorted. It does not fail under a demand for hot water.

mike787
February 2010

Sorry, my hopes have been dashed, not the flow or return sensors, even a new circuit board has not fixed it. The sensors are about £30, the circuit board is around £200. So what next? British Gas are coming back and in the meanwhile we have to keep resetting, thankfully it allows us to do that, though we are doing it about 4 times in the evening! What we have noticed is that the boiler burns, gets the house up to temp and then stops, as it should do. However, when it gets the signal from the thermostat to start again, it doesn't. The information for the code in the Vaillant handbook is so vague, it litterally could be ANY electrical component, fan, pump, etc etc, my fault seems to happen on re start. Fed up or what, the good thing is that British Gas come when they say they will and thank heaven for their service plan.

mike787
January 2010

After re setting mine over a few months, the code started to appear more frequently, rendering the boiler unreliable. I have found out my fault was either the flow or return sensor. It took British Gas just a couple of minutes to replace both of them. Since then, touch wood, no problems. I have no idea how much the sensors cost nor where they are in the boiler but the engineer said it was a very quick and easy job to replace them, he also changed both at the same time. Saying it would have been a waste of time trying to find out which one was at fault, if not both.

mike787
December 2009

I have exactly the same issue. I switch the unit off and turn it back on again and all is fine for about a week and then it happens again!! Any ideas on the route cause?

Mr C
January 2009

I have just had this showing on mine, major panic, no hot water or heat though the controller says the unit is fine. I simply switched off the boiler at the control panel and switched it back on again, hey presto all is fine! The manual says it is an electrical short. I'm leaving well alone now and have now signed up for emergency cover on it! I am not corgi registered nor a plumber nor affliated with the company who make Vaillant combi's. I guess I have been lucky, this time.

mike787
December 2008

check the boiler manual to see what this code means.
if no manual phone valiant up and ask for technical and they will help,they are great with after care.

little legs
November 2008