Optima 701 buzzing at ignition

[Steveham]

My Optima 701 (I know, I'll change it one day soon!) has developed a buzzing noise intermittently at ignition. If the boiler is off and the room stat clicks it on, or a hot tap is turned on it makes a buzzing sound for a couple of seconds. It lights and works normally, and tends to happen more often when it's cold, or hasn't been used for a while, like in the morning when the heating is turned on for the first time.

Anyone got any clues what is buzzing? It sounds a bit like a cross between one of thos joke shop hand buzzers and a wind up alarm.

 

[Agile]

May well be the gas valve.

May be caused by an impending fault on the PCB though.

Its probably harmless enough and can be ignored until you change the boiler ( overdue! ).

You could probably find it by using a mechanical stethescope or just a long stick etc.

Tony

 

[Slugbabydotcom]

May be caused by an impending fault on the PCB though.

I'd go with that one as most likely. You can often see blackening at the switching end of the relay where theres a clear plastic cover. A new PCB is fairly expensive but often worth replacing when the boiler doesn't have too many other issues IMO, even though these combi's are now getting on a bit.

 

[Agile]

I was really thinking of the smoothing capacitor on the PCB failing as that causes 100 Hz ripple on the supply line which causes the mod coil to buzz when its on full power.

Tony

 

[Steveham]

OK, first chance today to strip down and look at it, it's the relay sparking across the connection.

Sods law - I found it today, and tonight it has stopped completely! It is a SCHRACK RP420048 relay on the PCB, does anyone know if I can just replace the relay or if I need to get a new/recon board?

Not sure whether it just pins in or needs soldering - if it does need soldering I am not sure how easy it is to get the board out!

Great, just as it starts to snow - good job I have a real fire. My 5 months preganant wife isn't over the moon though, when I told her I wouldn't be able to get the bit until at least Tuesday! Grateful for any help fellas, ta.

 

[kev_1911]

maplins for your relay, board comes out fairly easy on the 701,mark all your plugs and connections(for replacement) i think 5 or 6 screws hold it down, if its soldered and you feel able to do it just bare in mind to be as speedy as possible with the iron as heat transfer to other componants and damage is likely,however a new board is approx £180/£200 you have alot to gain by having a go at repairing it. relay= £10 or £20 ? plus you time which is freeeeeeeeeeee.

 

[Agile]

That seems to be a 48v relay!

Maplins mainly have 12v and sometinmes 24v as those voltages are most often wanted by enthusiasts whereas most industrial applications use 24v and 48v relays.

Most likely to be available from RS or their retail name equivalent.

Tony

 

[Steveham]

Exactly right, it is a 48v job - and neither Maplins nor RS seem to carry it. RS have got the 12 and the 24 but not the 48, although the technical guys aren't in till tomorrow. It's listed on Tyco Electronics so I will try them tomorrow. Any other ideas?

I did manage to get it off, needed soldering, so hopefully it works if/when I get a new one.

Fingers crossed, I'll let you know - and thanks.

 

[Agile]

Sometimes you can clean up the contacts but most often the strip has been detempered and lost it springiness.

Tony

 

[Steveham]

Def not with this one, so bad it has started to melt the casing.

 

[Steveham]

Gaaah! How about this then, I have replaced the relay (after getting in touch with the German manufacturer!), replaced it, refitted the board, switched on and the same relay is buzzing, same contact. What does this mean now!

 

[Agile]

Like I said much earlier on, the main smoothing capacitor may be failing and allowing 100 Hz ripple onto the supply.

However boiler PCBs often use funny circuits like the GW Compact 80 which uses a diode and series resistor off the mains with a 10 uF capacitor across the coil to do the smoothing. I think the usual fault there may be the diode goes short circuit.

Tony

 

[kevplumb]

ohh should we be dishing out advice to an OP that might not be registered

for electrics or gas

 

[Steveham]

Don't worry Kev, I know my limits! I am happy with electrics, and replacing a relay on a board is school physics stuff, but when it comes to gas, water AND electricity I call in the experts - bizarrely I had a big leak from the boiler last night, hours after it had been left alone, so I have called in the professionals. I would imagine likely outcome is replacemnt of the old boiler, as first discussed long overdue!