Ideal icos m3080 blowing fuses

29 Dec 2004
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United Kingdom
Have the above boiler blowing fuses then ruins the circiut board, checked fan (108 ohms on the red- blue ) and gas valve all seem ok. after 10 mins its blows the 3.15 A fuse along with the pcb.

any ideas

apart from get a new boiler, this ones only 2 years old and the customer has also a isar combi also
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Did you check the pump ( assuming it has one inside or feeds power to it ) ? Most likely cause of overloads!

Pump is external along with controls, boiler is switched on with pump by controls, no pump over run fitted.
Run mains components independently, from a plug-in lead with 3A fuse fitted. The plug-top fuse will be a lot slower than the 20mm quick blow ones, so you might see smoke coming from the offending component first, but that'll tell you which one it was...

An insulation tester would probably get you the answer more quickly, as they would do a flash test at a higher voltage.

DOn't forget things which have mains on and are connected to earth, like hi limit stat.
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Is that boiler allowed to be used without a pump over run?


Just remembered.

I once went to one of these with a fault in the potted mains filter. It had failed and reflected a surge into the PCB which blew it.
In that case the filter had remained blown though.

Its the only one I have ever encountered but just possibly ???

Dont blame me if this long shot is NOT the cause in your case but why not apply mains to the filter with the PCB disconnected and leave it on all day to see if it blows the supply fuse.

However you probably meant it was blowing the internal 3.125 A fuse on the PCB. There is probably a surge supressor after the fuse. These can "operate" meaning go short circuit at lower volts than the rating if they are faulty or have been overheated.

When you say it "blew" the PCB, can you describe the exact failure point so I can see what that part of the circuit does? Scan and email it?

Dont overlook external mains operated devices like room stats.

Thanks for input

Found main pcb connection on the neutral had melted partially, replaced connector, mains supressor/capacitor and fan has been running now for 12 hours, new fan has improved performance, no vibrations throughout house.

New pcb was not required.

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