Blown programmer

[andyandy2]

I've got an old system of Baxi back boiler and fully pumped system for heating and hot water.
Went to have a bath last night and no hot water, tried the boost button on the programmer nothing happened, Changed the fuse in the FCU and switched on, there was a bang and flash from the programmer and the fuse blew again.
I've checked it again with both heating and hot water switched off on programmer and it still immediately blows the fuse.
Removed the programmer from the base plate and can see some damage to a couple of small components.
Obviously going to need a new programmer but my question is could another part of the system cause this, boiler fault or motorised valve etc, don't want to fit a new programmer and wreck it
The programmer is a BOSS THERM on the label on the back its got LANDIS & GYR type RWB270

Any help much appreciated thanks

 

[Jackrae]

The simple answer is "yes"

Out of interest what size of fuse was in the FCU feeding your heating system.

Chances are that an electrical short circuit elsewhere has overloaded the programmer output relays and literally blown the contacts apart due to the FCU fuse being over-sized (say 13A)

A 3A fuse should be more than enough for a conventional CH boiler system..

 

[andyandy2]

It was only a 3 amp fuse, and I replaced it with 3 amp, what is likely to have failed

 

[pallen5000]

if the flash came from the timer and there are burn marks on it, I would say its just the timer at fault. A faulty pump or motorised valve doesnt normally blow the time clock.