FAILED PCB IN BOILER

[Bodgedbuild]

Is that a fuse underneath it on the picture too?

 

[Harry Bloomfield]

This could be a long shot but if you look at the PCB track going to the little blue thing I think you might find the main voltage in goes through that and out the other side, I think it may be wired in series. If that does appear to be the case, it might be a GMOV and it might just require replacing?

A GMOV would be in parallel, rather than series.

 

[Bodgedbuild]

A GMOV would be in parallel, rather than series.

I'm not disputing that, I still think it will be that and the fuse that require replacing and the little black thing underneath is a fuse. Here is a picture posted on a site that "repairs" PCB's, they have clearly simply removed the GMOV (and a capacitor), repaired the burnt track and called it fixed. I'd wager a bet that a new GMOV and fuse, on the PCB, possibly a burnt track repair and the board would be tip top.....

 

[Harry Bloomfield]

Is that a fuse underneath it on the picture too?

It looks like one, or rather a fuse carrier. The varistor should have blown that fuse in the event of a high transient, if there was one - that is the whole purpose of the varistor, to blow the fuse if the varistor goes short circuit.

To reply to the OP - no the MCB would not detect or trip on a transient over voltage, unless it was accompanied by an over current event too.

 

[Harry Bloomfield]

I'm not disputing that, I still think it will be that and the fuse that require replacing and the little black thing underneath is a fuse. Here is a picture posted on a site that "repairs" PCB's, they have clearly simply removed the GMOV (and a capacitor), repaired the burnt track and called it fixed. I'd wager a bet that a new GMOV and fuse, on the PCB, possibly a burnt track repair and the board would be tip top.....

Possibly, but I am not impressed with a PCB repair job which simply removes components without a valid reason - they have removed the 'GMOV' and C37.

 

[Bodgedbuild]

Possibly, but I am not impressed with a PCB repair job which simply removes components without a valid reason - they have removed the 'GMOV' and C37.

I quite agree, they have removed a safety feature, I put repaired in quotes, "butchered" would have been a better terminology!

 

[flameport]

For a quick validation of whether the MOV is the cause of the fuse blowing, cut the remains of the MOV off, clean any carbon off of the surface of the PCB and replace the fuse.
If it works, new MOV required.

Should not be run like that for any length of time, as the next load of transients will destroy other things on the board instead of the MOV.

 

[Harry Bloomfield]

For a quick validation of whether the MOV is the cause of the fuse blowing,

I think the OP is suggesting the fuse didn't blow.

 

[BS3036]

"The fuse has blown in the boiler rated 4a. The fuse in the main plug 3a has not blown."

 

[Harry Bloomfield]

"The fuse has blown in the boiler rated 4a. The fuse in the main plug 3a has not blown."

The control fuse on the PCB ought to have failed first.

 

[JohnW2]

... Should not be run like that for any length of time, as the next load of transients will destroy other things on the board instead of the MOV.

... assuming, that is, that the MOV was killed by a 'load of transients', rather than just being/becoming faulty itself.

Kind Regards, John