Boiler Fault

[vignon]

I have a Vokera Unica HE boiler which keeps giving me a 34 fault reading, (Fan tacho signal fault) Fuse OK, how can I sort this out.
Thanks in anticipation

[The Builder]

On some models there was a situation where water dripped onto the fan causing it to burn out. Since then, they've come up with a shield that protects the fan.

Not DIY I'm afraid. You do need a boiler guy to check it over. How old is the boiler. Their fans can be around the exceptionally silly price of £300. There may be the option of fitting a cheaper one from a different boiler, but it will depend on what the guy finds.

Of course it may not be the fan, perhaps a simple, cheap thermistor.

[vignon]

Builder,Thanks for your input,I've checked around the fan area no sign of water drips re-fitted the Heat Exchange cover maybe the thermistor?

[Hymie]

Although I have no details on this particular boiler – a common method of providing a cheap ‘tacho’ signal is to fix a disc to the end of the shaft with regular apertures around its circumference and place an optical sensor at the edge. If your fan is using such a method to provide a tacho signal, then it might be that the disc apertures and/or sensor have become blocked with dirt.

If fitted, closely inspect the disc apertures for blockages and carefully clean the optical sensor with a suitable cloth – wiping both sides straddling the disc face.

[The Builder]

A good post from Hymie...... obviously knows much more about this than I do. These boiler's fans are speed controlled. They work at several different speeds depending on the mode the boiler is in at the time. The tachometer is vital to fan control.
His idea is certainly worth a try :o)

[vignon]

To those who offered their help and knowledge I wish to thank you. At the moment fingers crossed the boiler has started working again.

[Hymie]

All the same – I’d have soft brush ready to clean the tacho disc which may be all it needs.

If you Google ‘optical shaft encoder disc’ you should find an image the type of device that may be fitted.
Of course it could be a sealed unit.

[vignon]

The Builder,the fault has come on again and water is dripping from around the back which as you say needs the shield on the fan motor.will get the vokera engineer out to fix.