Vaillant VCW GB 242E Tripping RCD

keyplayer · 10 Jun 2005

Seems like an electrical problem rather than a gas one, so I had a little look (yes I know, so don't!). Now, first of all the polarity of the electrics has been reversed for at least three years(when boiler was converted to natural gas) and has obviously been working. Sound right? Anyway, i've tried correcting and situation is thus.

With polarity reversed rcd trips immediately (on switching on boiler fcu)

With polarity normal, boiler tries to go through firing sequence, and trips the rcd when (in my opinion) the spark operates.

Boiler owner (a sibling) has booked corgi bod for 4 days hence, but in the meantime any thoughts anyone?

kevplumb · 10 Jun 2005

is the pump running

keyplayer · 10 Jun 2005

Thx Kev, I believe it is, at least till power goes which seems to be at sparking point.

ChrisR · 10 Jun 2005

For a start disconnect everything else on that elec board which is protected by the RCD. Lots of things leak a few mA, and the trip goes when you get to 30. So it might not be the boiler doing it all.

Agile · 10 Jun 2005

I am by coincidence going to an interesting problem tomorrow which another firm has been to for many hours across four visits, charged £400 and still failed to stop the RCD ( or RCCD ) tripping shortly after the boiler starts.

I expect to identify the fault within 25 minutes or less. But then I am going with my earth leakage tester which is a clamp on measuring down to 1 Ma. I doubt that I will need it and I expect my old Fluke 77 will be all that I need!

My first question in this situation is "How did you measure the polarity?"

I next wonder if you have actually reversed the polarity regardless of what you think you have done.

You have not described what the problem was which caused you to start playing with the boiler.

Tony Glazier

PS I assume the boiler was converted to natural gas from LPG three years ago?

PPS have you checked for an earth-neutral short ???

keyplayer · 11 Jun 2005

Thx to all for your time.

My first question in this situation is "How did you measure the polarity?"

Visually, live wire going to neutral terminal, neutral to live.

I next wonder if you have actually reversed the polarity regardless of what you think you have done.

I have reversed the wires, which concurs with boiler wiring diagram.

You have not described what the problem was which caused you to start playing with the boiler.

The boiler, when attempting to fire up is tripping the rcd.

For a start disconnect everything else on that elec board which is protected by the RCD. Lots of things leak a few mA, and the trip goes when you get to 30. So it might not be the boiler doing it all.

It's definately the boiler. Its fcu is spurred off the ground floor ring and I've tried unplugging everything on the ring to initially identify problem. With just the boiler effectively connected it stilltrips the rcd, which incidentally protects all circuits on the cu.

PS I assume the boiler was converted to natural gas from LPG three years ago?

PPS have you checked for an earth-neutral short ???

Not sure what gas the authority was using prior to natural gas. Have checked for an earth-neutral short, but only with a multimeter. Can't afford a megger! I suspect there is a leakage on the ignition system, but I'm not going to get too involved with it, as it is above me really. I was just wondering if there is a common problem with this particular model.

Thanks again to all.

keyplayer · 13 Jun 2005

No ideas then??

ChrisR · 13 Jun 2005

Suggest you measure the voltages rather than trust the clour of th wires unless you're certain. Use a multimeter - N-E should be about 0 volts, etc. Ask if you don't know how.

At the boiler, try disconnecting things which are the heavy electrical things, like the pump, fan, gas valve. Try to find what's tripping by elimination, thogh it isn't always as easy as that!

Agile · 13 Jun 2005

For safety NEVER visually assume anything! The green wire might be the live !!! Testing is the only safe and successful method.

Test with a voltmeter between a pretty certain earth like a water pipe to each of the THREE mains inlet wires, earth to confirm it is connected, neutral and live. Only then consider touching the appliance.

My visit on saturday was to a boiler which the manufacturers agent has sent three people to on four visits. It was solved in a very relaxed ( to build up the drama ) 22 minutes using a £9 pocket multimeter.

I later used the clamp on earth leakage tester to show the 25 ma leaking to earth from the boilers external thermostat connections which are effectively at mains live.

Tony Glazier

keyplayer · 14 Jun 2005

Point taken, I didn't actually word it very well, I meant visually at the boiler terminals. I had already identified the live for certain by tracing it from spur at the back of a socket point, through fcu dedicated to boiler and through timeswitch. So, unless the whole circuit was reversed, which I have now confirmed not to be the case with a pocket mm, my original assumption was correct.

Agile · 14 Jun 2005

For safety NEVER assume anything.

The wiring to the spur may be reversed! Or the neutral may be disconnected!

I was once called to a boiler which was not working. It turned out the house wiring had been reversed previously and the installer had fitted the boiler to the wiring as it was in order to make it work.

Householder's father, an electrician, had corrected the whole house wiring error but failed to guess the boiler might be polarity conscious, after all other household appliances are not!

Tony Glazier

keyplayer · 14 Jun 2005

And this particular model? I'm assuming not polarity conscious?

keyplayer · 14 Jun 2005

Chris and Agile, thanks 4 the input. (I hope) you'll be pleased to know that my instincts were correct, and I have traced the earth leakage to the ignition coil(excuse terminology if incorrect). There is continuity on the coil between the live pin and earth pin, albeit with a resistance of approx 1.3Kohms, but this is clearly enough to upset the rcd, and some evidence of the unit overheating (scorched case!) Temp. borrowed another coil to try and all ok. Couple of questions though;

1 Are these units prone to failure?

2 On 12v vehicle ignition systems, the coils are prone to overheat if the primary circuit is energised but engine not running ie secondary circuit idle. Is this similar on boiler igniters? If answer is yes, does this indicate a problem elsewhere eg on pcb?

3 Could long term polarity reversal be responsible for spark unit failure?

ChrisR · 14 Jun 2005

1.3k is very low, I'm surprised a fuse didn't blow as well - maybe the rcd was too quick.
Yes high voltage coils break down. "Often" is a relative term, some will never go. Have known 2 go on newer vaillants than yours. In those cases the transformers were industry standards and putting new ones in cured the boards.

Car electrics were pretty primitive. The time the contact points were closed was set on the distributor and measured by dwell angle. That was OK as long as the thing was spinning. If you left the ignition ON when the car was stationary you could be unlucky, if the points were closed then the coil was connected, for as long as you left it.

The vcw boards were fairly reliable I believe, so there are lots floating around which have been taken out of old boilers, but it's only blokes like us who would keep them! I know one boiler breaker, in S London not good at posting thingsthough, I'm told!

keyplayer · 14 Jun 2005

Thanks ChrisR, most informative!

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Vaillant VCW GB 242E Tripping RCD

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