Myson Orion "Boiler" a Real POSER of a problem:-(

[Rick]

Hello I have a real poser of a problem for all Myson Orion experts! My CH/HW system is a conventional fully pumped syatem comprising Myson Orion

40si boliler, pump HSA3 position valve, room stat, cylinder stat and potterton programmer all conventionally wire for a fully pumped systam. The boiler is 12-14 yrs old and up to last week has been working OK. An earth fault has now developed on the system which trips the RCCB when the system has been running for approximately 10mins ie when the system gets hot - with demands from either CH or HW or both. So far I have * renewed the boiler thermostat * renewed the pump * renewed the room stat * run the system with only the pump and boiler in circuit * run the system with with all other lighting,power, cooker circuits switched off ie only the circuit feeding the CH/HW system on, and the fault still exists. Now here is the POSER. The system will run OK ie not trip when all the bottom sets of cover plates which surround the thermostat, ignition pcb and ignition valves are removed and/or left dangling - if you know what I mean. H...E...L......P!!!! my 7month old son is going to be very cold and Northern Gas have just quoted me £2200 to replace the boiler.

Rick

[r.p.mcmurphy]

try replacing each panel at a time...obviously one of the panels hold an item that is leaking to earth.

steve

[Ed Sirett]

You seem to be saying that you have definitely narrowed the problem to the boiler itself. Do you have any indication if the fault is to earth or a short circuit?

Can you see if there is any evidence of arcing or such like on the cover plates, or nearby?

I take it that because you talk about switching off other unrelated circuits that this might be a whole house RCD trip rather than just the boiler (socket ring?) circuit. If it's an RCD trip then the fault has to potentially include a direct Earth-Neutral connection.

HTH

[Pete C]

Are the thermostat, pcb valves attached to these plates or are they just covers?

cheers, Pete.

[Rick]

Hello Pete et.al. The bottom cover plate of the boiler which has the circuit diagram - of sorts - has nothing attached to it and is removed completely. The cover for the ignition p.c.b. is plastic and carries the thermostat control/regulator. There is a further small bottom plate to the p.c.b housing which carries a plastic connector block which is insulated from the plate and it also carries a supression capacitor. The latter two are the ones I have dangling from the wire to the thermostat and the terminal block. Hope this assists you in the fault find!!! :-) Rick

[Rick]

Hello HTH Very interesting! You are correct! The sub circuit from the consumers unit is a radial circuit protected by a 15A excess current circuit breaker and this does NOT trip under the fault. You are correct again the RCCB which trips - the only rccb - is in the consumers unit - which I assume also acts as a douple pole switch for isolating my electrical supply? The only indication I have that it is an earth fault -intermittent remember - is that it is the rccd that is tripping not the 15A sub circuit c'ct breaker????? If it were the latter then I assume it would be a short circuit????. The fault seems to be temperature related since the boiler runs for 10mins or so before the fault occurs. It's as if a component, connection or cable is failing due to heat. No there is no evidence of arcing anywhere. Hope this helps you with the remote fault find!!! :-) Rick

[Rick]

The plate that covers the ignition pcb is plastic and it carries the thermostat.... I assume that this would not be a problem. The bottom cover plate to the boiler is a cover plate and carries no electrical wires or components and it is completely removed. Neither can it interfere, foul or touch any wiring when it is fitted. The only plate that does carry electrical components - ie a terminal block and a capacitor - is a/the small removable plate which fits to the bottom of the pcb ignition housing. I will do as you suggest and wait to see what happens! :-) Watch this space!!! Thanks Rick

[Pete C]

Hi,

My immediate guess is that the supression capacitor could be faulty, try replacing the small bottom plate with it connected or disconnected. If all is well replace the other plates one by one, first with loose screws then tightening them up.

cheers, Pete.