Not something I’ve seen before…

[CBW]

It may be worth metering the resistance between N and the other terminals - hopefully you haven't got a batch of these that have some sort of defect, or you may be getting a few more call-outs...

Aye, might try that tomorrow. We have recently ordered in the region of 50 of these give or take a few, so I do hope not a bad batch! Albeit, some are used as direct link up to intergas (so no receiver).

 

[CBW]

So measured resistance as OL between N and other terminals, tried continuity buzz too only got that between L and A which is correct. Maybe it’s one of life’s mysteries?

 

[lloyda]

What's the other half of the BDR91 look like? Any components in that area that might have overheated/burnt out?

 

[CBW]

What's the other half of the BDR91 look like? Any components in that area that might have overheated/burnt out?

I don’t recall seeing anything, but it’s in the back of my van, will check at some point, thanks.

 

[CBW]

What's the other half of the BDR91 look like? Any components in that area that might have overheated/burnt out?

Good shout on this, but still non the wiser, as the overheat/scorch is what appears to be between a and a?

 

[lloyda]

It looks like the heat is coming from what are most probably two diodes that are disappearing under that white plastic cover, (Photo of another BDR91 without cover for reference.)

 

[RandomGrinch]

It looks like the heat is coming from what are most probably two diodes that are disappearing under that white plastic cover, (Photo of another BDR91 without cover for reference.)

Good call, thank you, I hadn't looked closely.
Yes, those diodes have let out their magic smoke!

And a common failure mode for diodes is to short.

So some conjecture: the issue was internal to the BDR91, causing excessive current draw through its power supply.
The loose strands of wiring at the boiler, would likely not have caused this failure.

 

[RandomGrinch]

So measured resistance as OL between N and other terminals, tried continuity buzz too only got that between L and A which is correct. Maybe it’s one of life’s mysteries?

...and too late, but just for clarity, I meant test the terminals on the back of the BDR91, not just the backplate!

 

[CBW]

...and too late, but just for clarity, I meant test the terminals on the back of the BDR91, not just the backplate!

I’ll try it at some point, as I’ve still got the bdr91.

 

[RandomGrinch]

I’ll try it at some point, as I’ve still got the bdr91.

If you can take a photo of the PCB, we may be able to tell more.
This could be an item that Honeywell may be interested in investigating, especially as 'you' are a bulk purchaser...

 

[CBW]

If you can take a photo of the PCB, we may be able to tell more.
This could be an item that Honeywell may be interested in investigating, especially as 'you' are a bulk purchaser...

As requested

 

[RandomGrinch]

As requested

Thank you.

That really is quite impressive!
They have obliterated themselves - I believe you may find a dead short between pins E1 (N) and E2/E3 (L/L)
I can't see damage to any of the other components though - some resistors look scorched, but that only seems to be from smoke travelling upwards within the BDR91's case.
To me, there is nothing obvious on the board to suggest what caused this.

I would send the pic to Honeywell, and see if they are interested in investigating.

 

[CBW]

Thank you.

That really is quite impressive!
They have obliterated themselves - I believe you may find a dead short between pins E1 (N) and E2/E3 (L/L)
I can't see damage to any of the other components though - some resistors look scorched, but that only seems to be from smoke travelling upwards within the BDR91's case.
To me, there is nothing obvious on the board to suggest what caused this.

I would send the pic to Honeywell, and see if they are interested in investigating.

Thanks @RandomGrinch, I’ll send it to my lead engineer/gas manager as they have a contact at Honeywell. Meantime I’ll test those pins.

 

[CBW]

Ok testing pins between the following:

E1 and E2 - OL cont buzzer
E1 and E3 - OL cont buzzer

E1 and E2 - Ohms resistance - 5.50M ohms

E1 and E3 - same scale - same result - 5.50M ohms

I’ve been since spoken to another engineer who’s had the same problem! His was installed approx 9 months ago, so I’ve aired my concerns to Honeywell, will let you know if there’s an outcome.

 

[CBW]

Just an update on this, I returned x2 faulty receivers back to Honeywell and they concluded they couldn’t find anything wrong with them! Apparently, the scorched area’s are fuses and could have been from spikey incoming electrics.