Boiler tripping 3amp fuse

[GgSumo]

Hi

have Worcester boiler 4 years old that trips the 3amp fuse but only when a working room temp sender box is fitted. Story is we had boiler issues with condensate pipe which has all been repaired but meant that the 3amp spur and the sender (Honeywell bdr91) got wet. Boiler put backinto full working order, will stay on for hot water and can push the heating boost button (man with ladder) that runs for 15 mins all without any problem as long as broken sender unit is installed (so obviously no heating as no call signal)

replaced the front of the sender unit with exactly the same type and everything worked for about 30mins then bang. Reinstalled broken sender unit and New fuse fitted this morning and boiler back on with no issue with hot water and boost function running Heating (15 min cycle).


So my question is what reading should I get from the sender unit wiring any ideas what to do so I don’t blow another 70 quid unit. Is it likely something shorting to earth and if so why take half an hour to blow? It looks like it’s probably blown the board in the sender again as there is a black mark on the 240v side of the sender unit.



Hopefully this is something simple I can sort so any help appreciated otherwise will get them to send a leccy to sort next week. Obviously I know I cannot open boiler so it’s what I can check at switch, thanks

 

[ianmcd]

can push the heating boost button (man with ladder) that runs for 15 mins all

That is not a boost button , it is called chimney sweep mode, it runs the boiler flat out for 15 mins and ignores all controls to allow an engineer working on the boiler to run tests , stop pressing it, forget it is there, it is not a user control

 

[ianmcd]

but meant that the 3amp spur and the sender (Honeywell bdr91) got wet

Do you actually mean the RECEIVER and not the sender ? the sender is the thermostat with a digital display

 

[GgSumo]

Yes sorry receiver wired to the boiler

 

[GgSumo]

That is not a boost button , it is called chimney sweep mode, it runs the boiler flat out for 15 mins and ignores all controls to allow an engineer working on the boiler to run tests , stop pressing it, forget it is there, it is not a user control

Thanks, only pressed once to check it it tripped the fuse or not. Boiler is only on currently for hot water

 

[ianmcd]

If the boiler ran OK with that presssed the problem is not with the boiler, did you read my post about sender and receiver

 

[GgSumo]

If the boiler ran OK with that presssed the problem is not with the boiler, did you read my post about sender and receiver

Yes answered above, yes sorry the receiver wired to boiler, thanks

 

[ianmcd]

Yes answered above, yes sorry the receiver wired to boiler, thanks

try removing the cover and blowing through the L&N terminals with a hairdryer, the A&B wouldnt blow a fuse, no harm in using the hair dryer on the rear of the fused spur too, sounds like you still have some moisture in somewhere

 

[GgSumo]

try removing the cover and blowing through the L&N terminals with a hairdryer, the A&B wouldnt blow a fuse, no harm in using the hair dryer on the rear of the fused spur too, sounds like you still have some moisture in somewhere

thanks Ianmcd I changes the receiver and trimmed and cleaned the wire. It had definitely arced between live and neutral. Also cleaned out and hairdryered the 3amp spur. Heating has now been back on since yesterday afternoon. Thanks for the advice