Curious sequence of events

[timhoward]

1 - Major supply fault, details unknown. By time I get there DNO already put in genny and are digging up road.
2 - Reason for call, heating not working. I find Horstmann heating controller and Glow-worm boiler completely non functional, I bypass controller and change 630ma fuse on boiler PCB and all comes to life. All three zone valves and pump are working.
3 - DNO repair supply cable, and cut over back from genny to grid.
4 - Fuse on boiler PCB blows a 2nd time when power restored. Boiler was switched off at unit, but not at FCU

Fuse on PCB doesn't blow when heating system energised while calling for heat, tried multiple times.

I'm trying to decide if the direction of travel should be:
1 - high propensity to surges, get an SPD fitted
2 - some intermittent fault on heating system that I've missed randomly increasing draw on boiler PCB, e.g. possibly pump or fan on way out.

Any thoughts? I'm erring on 1 as it seems too much of coincidence.

 

[timhoward]

I've now replaced the programmer, and also the FCU as it started springing to the on position itself!
I guess I now wait and see if the boiler PCB fuse blows again in the near future or whether this was all a series miscellaneous events.
As it was a Starbreaker CU it made adding an SPD a quick and easy no-brainer.

 

[pc1966]

Having SPD is not going to do any harm and might just help here, certainly for other surges, etc.

One question about the fuse is the replacements of the same type as well as current? Some have speed ratings such as T (time delay), F (fast), and FF for very fast / semiconductor protection.

 

[timhoward]

One question about the fuse is the replacements of the same type as well as current? Some have speed ratings such as T (time delay), F (fast), and FF for very fast / semiconductor protection.

You have probably nailed it.
The original was a type T and both replacements were also intended to be this.
But the 1st one did come from my random bits box and you've got me wondering if I mis-read an F for a T.
The 2nd one came from a box at home and is definitely correct.
It's a nice theory to cling to in the meantime anyway. I don't still have the 1st replacement so will never know for sure.

 

[SagaCU29]

You have probably nailed it.
The original was a type T and both replacements were also intended to be this.
But the 1st one did come from my random bits box and you've got me wondering if I mis-read an F for a T.
The 2nd one came from a box at home and is definitely correct.
It's a nice theory to cling to in the meantime anyway. I don't still have the 1st replacement so will never know for sure.

When we went on holidays I would turn off the boiler at the FCU on return would turn it back on to find there was no supply
it had blown the fuse in the PCB this happened a few times, this was a Baxi 105 not sure if I was turning it back on when it
was calling for heat that might have pushed it over the edge!