Voltage to boiler fan 'drops out under load'

[Rockingit]

Just had a call from an M&E client of mine and good mate asking to pick my brains.... large 3ph biomass boiler with (I assume variable speed) 1ph fans internally. Says he's got 230v L-N/E on the connecting plug but when the fan gets connected there's nothing on the internal fan connections. So I says "knackered fan or cable" - "Nope, changed it for a new one". So then I says "Well it could be a triac died on the controller board and all you're reading is a phantom voltage and it's disappearing under current draw". "Nope, I thought that too, changed the controller board as well". He's going back to his workshop to mess about plugging a fan directly to 230v just to check it, but can anyone think of any quick pointers?

 

[snowhead]

Bad connection on a 230v isolator for the fan, if there is one.
Bad connection / failed motor overload.

When he finds the motor works on 230v direct he needs to go back the the source of the 230v, presumably in a control panel, stick a meter on the 230v and watch what happens.
If it stays 230v keep moving forward on the 230v line towards the fan and test again till he finds a point the 230v is disappearing.

 

[Petej999]

wrong sized cable causing excessive VD on circuit