Vaillant 824 problem

[mihai]

My Vaillant turbomax has just developed a fault (by no means its first!!) and I thought I'd seek some advice before shelling out my hard-earned!

It has, out of the blue, started to be unwilling to provide hot water. The central heating side is fine but the diverter doesn't even flinch when the hot taps are used. I'm guessing that it isn't sensing the demand for hot water.

I have already (over a year ago) fitted a new diverter valve and repaired the fan pressure switch and I'm confident that the fault is not in either of these as the diverter valve can be seen to move easily through its full range on startup and the boiler itself works fine on the heating side.

Any ideas

M

 

[gastight]

Does the microswitch on diverter get activated ? Test the microswitch

 

[chrishutt]

Not sure about Turbomax offhand, but there must be some sort of flow switch that detects the mains water flow? This would be the obvious thing to check.

What happens if you put the HW preheat on (turn HW temp dial to extreme clockwise position and return)? If the preheat works that might enable HW even if flow switch is faulty.

What do the Status (S) codes say (what does the boiler think it's supposed to be doing)? Any Fault (F) code? If it's a Turbomax Plus, you've got brilliant diagnostics available. Use them.

 

[mihai]

Thanks all

Sorted now

It was the flow sensor - it has a magnetic pickup which senses rotation of a vane inside a brass housing. There was a thin layer of scale inside the housing which was presumably stopping the vane from turning. A quick clean and a scrape and it's working just fine now

 

[Agile]

Gastight, I have never seen a microswitch on the diverter valve on an 824

Tony

 

[mihai]

That's because there isn't one

It's just a ball valve with a stepper motor actuator controlled by the PCB.

Still, all is well now - for the time being

I've not been impressed with the overall reliability of it since the first diverter went tits after little more than a year and the fan switch going a year later. At £80 for a diverter and about £50 for a switch (I disassembled the 'sealed' unit and cleaned the contacts rather than replacing it) the spares are not cheap and really I'd expect components like these to last a bit longer.

The old boiler we had was a real dinosaur but only ever needed a bit of a hoover out once in a while to remove dust and soot. The Vaillant does burn very clean though.

 

[Agile]

Yes, I do know whats in your boiler!

Unfortunately the diverter was a serious problem because the ball swelled up with certain common water treatmant chemicals. Usually at 18-20 months.

Now the square black air pressure switches are starting to fail. I changed two last week. They have changed the design.

There have also been some PCB failures too although I have not seen many myself but the spares place told me they sell a lot but thats often due to mis diagnosis.

And people think Vaillant are reliable boilers!

Tony Glazier