Vailant combi boiler

[musicmalc]

I have a problem with a vaillant combi boiler with the digital temperature sensor which occasionally seems to fluctuate and flicker wildly. This also seems to cause the odd lockout of F64 (Electronic failure) which is usually fixed by resetting the on/off switch. I have had a Vaillant engineer who has replaced one of the flow sensors, but this has not cured the problem which still seems to happen randomly, without warning. I am reluctant to call the engineer back until I have a better idea of what possibilities could cause these things to happen.
Any ideas?
Malcolm

 

[gas4you]

I would check both sensors and/or replace, also check wiring to them for shorting out somewhere. If this fails I would start to suspect the pcb.

Unusual on these I've found, but as it is presumably under warranty it could be replaced.

Hope you got a proper Vaillant engineer and not a group service Glow Worm numptie

 

[musicmalc]

Thanks for the advice dave.
I checked the reistance on all three sensors (removed) which was identical, so I presume they are ok. I do have a spare which I bought off the engineer who came as they seemed pretty easy to install. I may exchange them one by one and test run for errors in case there is another breaking down under stress. I will check the cable runs to these also as you recommend.
I'm afraid it's not under warranty any more, it is at least 5 years old, hence my reluctance to keep bringing an engineer in. (He was Vaillant approved)
If the NTC's are not the problem I will change the PCB. It may have been damaged by a faulty clock which was recently replaced by a radio controlled one.
I notice the PCB has been upgraded from the original part specification to a newer model. perhaps my older model had some faults built in.
Malcolm

 

[gas4you]

I would suggest a fixed price repair by Vaillant as your 'approved ' engineer can't find the fault.

I am classed as Vaillant Approved, but this does not mean I know how to fix them all, just an excellent installer

My mate who is a time served Vaillant engineer finds solutions to faults that I would never dream of in a million years

 

[bengasman]

I would call the engineer back. You paid for repair and the fault is still there, you should get at least a partial rebate or deduction of price for repair. Intermittent faults can be difficult to find so it does not mean your engineer was negligent or incompetent. Any reputable engineer will come back if his work turns out to have no result, unless he told you in advance that it might not do the trick.

 

[musicmalc]

Thanks Dave. I did ring the engineer back. He was surprised as he did say the NTC was definately not showing any reading and was the likely fault. He also said the same as you. That he would check the loom wiring in case there was a short and bring a replacement second hand PCB which he knows is good to allow me to use it for a period to see if this fixes the problem. He is an engineer who was given to me by Vaillant, certainly not cheap, and admitted to me that Vaillant just recommend replacing any suspect parts. (Not surprising with the cost of some of them!) He said he would not charge further and only for a new PCB if the test one proved to work OK, further stating it wasn't his policy to change perfectly good components. - My God an ethical repair man! Now there's something new.
Thanks again Dave