Boiler fuse keep blowing

[ThatchedPhil]

We had a power cut recently and boiler (old Potterton oil boiler) went dead and realised fuse inside boiler had blown. Replaced fuse but every time switch on boiler it blows again immediately. Struggled to get a pro to look at it but one did and traced it to motor on the burner. When the burner was disconnected from the control box could switch on boiler, control panel light up etc. and fuse doesn't blow. So bought a new motor and connected it but still fuse keeps blowing so guess it wasn't the motor after all. What else could it be? The little Honeywell control box with the reset button?

 

[oilhead]

What model boiler? What burner is fitted? As the fault appears to be isolated to the burner, this leaves the solenoid coil, transformer or control box. The first two are easily checked with a multimeter, and a control box fault is usually accompanied with scorching, but can be traced with a multimeter across the various terminals. You check for a live terminal down to earth.

 

[ThatchedPhil]

It's a Potterton Rapido boiler and I think the burner is Nu-Way. Thanks we were thinking solenoid, transformer or control box so glad to have that confirmed. No multimeter and not sure what to check for (!) but might try replacement control box while waiting days for next engineer. Had two already and 9 days no boiler.

 

[Terrywookfit]

Disconnect coil and transformer in sequence until fuse stops blowing.
My guess would be the tranny

 

[oilboffin]

I'm with T the look at the tranny it might be bubbled up and you can tell at a glance.Bob

 

[ThatchedPhil]

Ok thanks will have a close look at it this morning.

 

[ThatchedPhil]

...

 

[oilhead]

I'm with T the look at the tranny it might be bubbled up and you can tell at a glance.Bob

On a Nuway burner on a Rapido, the transformer is likely to be a conventionally wound unit, and will not 'bubble' up in the same way as an EBI. You may see some evidence of the pitch leaking. If it is the transformer, you need to look a little further to replacing it, as you may have another fault which is causing reignition, and thus overloading the unit.