Baxi 105e keeps blowing fuses

[martyb1965]

My Baxi 105e trips fuses in the fused spur when running hot water whilst central heating is running. It doesn't happen every time but has done this about 10 times in the past two months. I fitted and RCD protected fused spur but this hasn't tripped indicating earth leakage, it blew the fuse again indicating pump overload?
The system is running nicely at 1.5bar and rises slightly to no more than 1.7 bar when the hot water tap is turned on.
Please help.

 

[bengasman]

Unlikely to be pump overload.
Probably loose wire. Check connections to pump

 

[martyb1965]

Thanks. I have checked all connections from the pump to the pcb to the fused spur and beyond and all are secure.
It hasn't tripped in 24 hours and I ran a bath with no fault. Surely there must be something serious enough to blow a 13a fuse when it DOES go? (I know there should only be a 3a in it but I ran out.)
Is there a sudden excess load placed on the electric supply/pump at the point when the hot water tap is switched on?
There is a small fuse on the pcb which always remains fine and thats not 13amp. I am beginning to think that there could be too much load on the whole 30amp ring main?
I'm just clutching at straws now....

 

[gas4you]

Check the fan.

Are there any internal leaks dripping onto any electrical components?

Check the DHW microswitch to see if the small 'o' ring has gone on the actuating pin.

 

[martyb1965]

Thanks. I will check the fan. There is no water leakage visible and surely if there were, the rcd protected fused spur would trip which it isn't.
Does the fan only operate when the burner is going?

 

[martyb1965]

The fan is running freely with no problem. It hasn't blown a fuse in three weeks until tonight when it blew 3 in a row. I have discovered that it blows only when the hot water tap is turned on and not the central heating. It is now working again for the moment. Please help!

 

[baxpoti]

Replace the DHW microswitch.

 

[martyb1965]

Thanks, I will try that. If it helps your diagnosis, it only blows whilst in the middle of filling the bath. This means that hot water has began to flow for a couple of minutes and has then tripped whilst still flowing. When I try to change the fuse immediately after, it blows within a couple of seconds again. However, if I leave it for a short time, then change the fuse, it will go on for a few weeks and a good number of bath-fills until it blows again.
If water IS leaking onto electrical components, won't this trip the rcd and not blow the fuse?[/u]

 

[martyb1965]

How embarrassing is this??
I have just tried one of the fuses that I replaced yesterday (thought to have blown) in the spur and it has NOT BLOWN!!! What has been happening is the boiler has re-started when I re-connect the power supply after disconnecting it (i.e, like when you change a fuse).
The boiler shows all signs of power loss as there are even no lights present. I am wondering next time if I were to reset it (turn the selector to the "R") whether that might work? I still need to know why it is tripping during prolonged hot water flow.
Sorry for misleading you guys but it was just a chance find.