Vaillant Turbomax 828 (628?) combi - fault found and fixed - for reference

[eeyore.is.here]

Just for reference, in case anyone has the same problem, my Vaillant non-co= ndensing Turbomax 628 or is it 828 ? combi, now 9 years old, has been a lit= tle intermittent lately, with hot water sometimes not coming through. Howev= er, it always fixed itself quickly. Not today.

The diagnostic code was S.33 wich points to the fan/pressure switch.

Indeed I couldn't pick up any voltage to the fan at the circuit board conne= ctor when I turned the hot water on or tried the CH. The pump ran, the dive= rter valve diverted etc.

The diagnostic booklet flow chart simply tells you to change the pcb at thi= s point.

I prised the plastic back covers off the pcb had a look. The central (mains= voltage) area smelt of ozone. Ozone meant sparking, but I couldn't figure = out what might be sparking. Well a few attempts at turning a hot tap on and= tapping things soon provided an explanation - greenish-blue arcing inside = one of three large relays (transparent cover).=20

Prising the transparent cover off allowed access and bit of a scrape of the= changeover contacts later (using wet and dry) and the relay closed without= continual fizzing and arcing (a slight spark but that's normal for an indu= ctive load like a motor). However, still no 240V at the fan motor connector= !

I isolated the mains and set to buzzing out the route between line at the m= ains LIVE input screw terminal, the relay contacts and the brown wire (live= ) on the fan connector (WITH A dvm SET TO AUDIO BUZZER) revealed that the c= ontacts were now making too light a contact to work. A bit of adjustment wi= th a fine blade on the live fixed relay contact soon brought the clearances= back into kilter and I now have hot water again.

I may have to replace that relay in future but I'll see how it goes.

A word of warning - to gain access to the relays you have to take a second = protective cover off the pcb, the high voltage bit. There are plenty of ter= minals at mains voltage including the mains transformer terminals which are= very in-the-way. Don't work on live mains equipment unless you know what y= ou are about.

[eeyore.is.here]

condensing Turbomax 628 or is it 828 ? combi, now 9 years old, has been a l= ittle intermittent lately, with hot water sometimes not coming through. How= ever, it always fixed itself quickly. Not today.

nector when I turned the hot water on or tried the CH. The pump ran, the di= verter valve diverted etc.

ns voltage) area smelt of ozone. Ozone meant sparking, but I couldn't figur= e out what might be sparking. Well a few attempts at turning a hot tap on a= nd tapping things soon provided an explanation - greenish-blue arcing insid= e one of three large relays (transparent cover).=20

By the way I isolated the mains before I started to poke around inside the = relay!

he changeover contacts later (using wet and dry) and the relay closed witho= ut continual fizzing and arcing (a slight spark but that's normal for an in= ductive load like a motor). However, still no 240V at the fan motor connect= or!

mains LIVE input screw terminal, the relay contacts and the brown wire (li= ve) on the fan connector (WITH A dvm SET TO AUDIO BUZZER) revealed that the= contacts were now making too light a contact to work. A bit of adjustment = with a fine blade on the live fixed relay contact soon brought the clearanc= es back into kilter and I now have hot water again.

d protective cover off the pcb, the high voltage bit. There are plenty of t= erminals at mains voltage including the mains transformer terminals which a= re very in-the-way. Don't work on live mains equipment unless you know what= you are about.

[The Natural Philosopher]

non-condensing Turbomax 628 or is it 828 ? combi, now 9 years old, has been a little intermittent lately, with hot water sometimes not coming through. However, it always fixed itself quickly. Not today.

connector when I turned the hot water on or tried the CH. The pump ran, the diverter valve diverted etc.

voltage) area smelt of ozone. Ozone meant sparking, but I couldn't figure out what might be sparking. Well a few attempts at turning a hot tap on and tapping things soon provided an explanation - greenish-blue arcing inside one of three large relays (transparent cover).

changeover contacts later (using wet and dry) and the relay closed without continual fizzing and arcing (a slight spark but that's normal for an inductive load like a motor). However, still no 240V at the fan motor connector!

mains LIVE input screw terminal, the relay contacts and the brown wire (live) on the fan connector (WITH A dvm SET TO AUDIO BUZZER) revealed that the contacts were now making too light a contact to work. A bit of adjustment with a fine blade on the live fixed relay contact soon brought the clearances back into kilter and I now have hot water again.

protective cover off the pcb, the high voltage bit. There are plenty of terminals at mains voltage including the mains transformer terminals which are very in-the-way. Don't work on live mains equipment unless you know what you are about.

WhenI bough t my old XJS about three of the relays controlling high current things like the heated rear window and so on had failed in the way you describe.

filing and buffing the contacts worked for another 5 years...till I sold it..

[geoff]

In message , [e-mail] writes

Fan control relay - back EMF of the coil

Turn the bugger off ... simples !

[ARWadsworth]

You should consider this sort of thing for a living geoff.

[geoff]

Hmmm , now there's an idea

[Man at B&Q]

Doesn't affect the contacts.

MBQ

[Man at B&Q]

Given that comment, I would not employ him.

MBQ

[Tim Lamb]

Yes it does. Maintains the arc for longer than for a resistive load would.

regards

[geoff]

In message , Man at B&Q writes

I was using noddy language in a noddy thread (a bit like people who misuse the term "dry joint") Its actually the energy stored in the fan coil when the relay contacts open arcing across the contacts that knackers the relay

Would I want you as an employer - I think not

[geoff]

Oh do f*ck off

[ARWadsworth]

Why?

[Man at B&Q]

Well, "Fan control relay - back EMF of the coil" implies the back EMF of the relay coil is somehow causing the isue with the contacts. It dosn't.

MBQ

[Man at B&Q]

Either he doesn't understand back EMF or he can't explain himself clearly. In this case the latter. If he'd said "fan coil" (a strange term in itself) then it would hev been clearer.

MBQ

[Tim Lamb]

Hmm.. I think you know what was meant:-)

regards

[geoff]

In message , Man at B&Q writes

No it doesn't you retard

I admit that I could have actually stated which coil I was on about, but I expected people to have a bit more of a clue than yourself and understand that I was on about the fan coil, as that is what the contacts of the relay are switching

People like you are the reason that manufacturers of toasters have to put warnings on them stating that it gets hot ... Get back under your bridge

[Man at B&Q]

Relays have coils. Motors have rotor or stator windings (maybe even both). Learn to use the correct terminolgy and we might get on.

MBQ

[Man at B&Q]

n

No, using the words "relay" and "coil" in the same sentence is very easily construed as referring only to the relay.

MBQ

[Tim+]

Bollocks. We (and you) knew that he was talking about an inductive load.

Tim

[geoff]

Not sure I really want to

Pedants who are stupid for the sake of it are not the sort of person I can be arsed with

I have better things to do with my time, like running a business which repairs boiler pcbs, for example