Vaillent turbomax lockout

[apexlets]

I have a Vaillent turbomax combi that goes to lock out on first start up from cold either on heating demand or hot water demand. Once manually fired up it will continue to stay on while heat is called for on the timer. In other words it only goes to lock out when system is cold. The system was serviced last August and it has worked fine since as it has always done. An engineer came out last week who couldnt find a fault but replaced a micro switch but the problem is still occuring.

Any advice or thoughts would be greatfully appreciated before I call out the engineer again and face another £80 call out charge

Thanks

 

[Agile]

I may get flack from my colleagues saying this but if he came and was unable to diagnose the fault then I would expect him to come again at no further charge.

Sometimes dirt in the pump makes it fail to start up when cold. This might well apply in your case and if there was no other obvious cause I would have cleaned the pump if I had attended.

You dont mention the actual model but I presume it has no diagnostic display?

Tony

 

[Boilerman2]

I had a T/max a few years ago doing exactly what yours is doing, it turned out to ba a faulty gas control valve, not passing gas to the burner quickly enough

 

[apexlets]

Thanks Aigle and Boilerman2 for your input.

The boiler model is VUW282E and does not have a diagnostic display - sorry for missing that out on my original post !

The pump runs fine at pre burner ignition even when the boiler is cold so I guess its not dirt !

The gas valve seems to operate perfectly once the boiler has been manually fired up on the overide/reset and the boiler starts to heat up.

As long as the boiler is left on heat demand it will run perfectly even on thermostatic switching - it is only when the boiler is fully cold that it goes to lock out on switched demand

 

[Agile]

Sometimes gas valves can stick closed EVEN if the solenoid coil is powered correctly. Thats particularly likely when cold and not having been used for several hours like in the morning.

Thats difficult to diagnose if you are not there and measuring applied voltage and gas outlet pressure simultaneously.

Tony

 

[Mozza00]

Could it be the flame picture electrodes that need adjusting?

Had similar fault on same boiler and engineer gapped to 4mm and worked ever since (touching wood).

 

[apexlets]

Thanks guys -- I will put your suggestions to the engineer and see if he will come back out (without a repeat visit charge) to check your suggestions for the fault. He is an approved Vaillant service engineer so I would have thought he would have known to check for those things but I guess there are good engineers, brilliant engineers and dare I say the below par ones - guess I got the below par one but i'll keep that to myself for the time being

Will post the outcome to let you know

Once again - thanks

 

[Agile]

To be fair to him, intermittent faults are very difficult to find.

I always consider what MIGHT be causing the problem. I can check the pump but the gas valve is impossible to check unless the start up conditions are established and the situation carefully monitored and you only have one opportunity to do that which is the first time its used each day and there is no guarantee its going to fault them.

Because I like to solve every boiler fault I would visit as many times at no extra cost and do whatever is necessary to solve the problem.

Tony

 

[Boilerman2]

Here is a top tip!!!! SWITCH THE BOILER OFF the night before, so your Engineer can actually see a Cold Start for himself, (if he has my luck , the blasted thing will probably fire up first time though)