Boiler relay buzzing/arcing


I have a relay in my boiler which buzzes/arcs I'm trying to diagnose the fault, probably in my wiring. What conditions (eg shorting) would cause a relay to switch on & off very rapidly (leading to a buzzing. noise) & arc?
All the thermostats/motorized valves function correctly. The condition occurs when the DHW reaches temperature, ie the cylinder stat opens.
Can't work it out. Any advice would be appreciated. Many thanks Jonathan
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Can't be specific, but it sounds as though your relay contacts are in series with the relay coil, i.e. when it starts to operate it disconnects the operate path and then releases, then operates, ad infinitum...
Peter
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What sort of a system is it?
http://content.honeywell.com/uk/homes/systems.htm
Y or S plan I assume.
If it is a Y plan then I would be tempted to blame the cylinder stat. It sounds like that it its contacts have failed.
On a S plan I would suggest the microswitch in the HW valve has failed
Adam
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On Fri, 27 Jan 2006 22:03:03 +0000, snipped-for-privacy@lineone.net wrote:

Peter Wrote:

Thanks- I'll investigate this.

correct terminals on the boiler out to the controls. Superficially, I can't see how this could then get swapped over to mix the contacts & power supply for the coil.
Would this condition be true when the cylinder stat is satisfied (break on temp rise), the arcing starts. It is definitely arcing - I can see it. I tried disconnecting the cyl stat & the relay immediately started arcing. If I up the temp on the cyl stat, the arcing stops.Some of the circuitry is hard wired in the boiler (system boiler) so it is not easy to work out what goes where. I've also got a programmable room stat on the same control circuit. I must admit, I had to think long & hard about marrying the circuit diags for the boiler, the motorised valve & the prog & cyl stats.
I wondered about the following diagnostic approach: presumably if I disconnected all the external controls, (valve, 2 stats) and used the unused boiler simple time clock in it's ready-wired configuration (I had to remove a loop to "break into" this control circuit), this would indicate if the fault lay in the relay, or my wiring? A nod would be appreciated, as this is a fair amount of work....
Adam wrote:

It is S plan. This is a possibility Iwould look at later as all new components. Chap at PTS assured me :*) that PTS Boss brand motorised valves made by Danfoss (or other big name) so I suspect my wiring first (more likely that I've wired the valve wrong), or I have a hunch about the relay.
Probably help to mention that this condition started from first use. Corgi chap did the gas stuff & test fired it - all OK, but obviously didn't hang around for ages until the water got to temp. All new components in CH system.
BTW, what is the correct way to get 6 or more cable cores/conductors from a boiler in one room to controls in another? The most cored cable I could find was 5. In the end I ran 3 lots of T&E & labelled the conductors at each end 1-6. Is that bad?
Jonathan PS If I had the cash I would get someone to look at it.
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