Not Plugged in.

Is anything else plugged into that socket ? It suggests that there is something on the load side of the switch,  that is required to complete the loop for the fan to work.

So what may be on that switch  - perhaps an N-E fault if the neon lamps 'flylead' has been pinched  or something in the back box is pressing on the sockety part of the back of the fitting.(DP or SP switch on that model I wonder ) or even an unrealised L-E fault if the CPC is off-earth.

I'd want to see behind the cooker control unit at this point. If that is not possible, plug something, ideally a socket tester into that 13A socket and see what it reckons is going on. Pay close attention to NE voltages. And as always when things do not stack up. assume everything  is dangerous until demonstrated to be safe.. I'm sure you know that. Casual readers may not.

It may even be that the fan is in effect in series with the cooker under certain conditions - does the cooker work as expected ?

M.

The cooker has been working fine until I came to convert the cooker outlet plate to a 13 Amp socket for a new gas cooker that needs ignition. My socket tester shows no problems.

The 13 Amp socket on the cooker control panel shows o.k. on my socket tester and powers a radio with no problems. The neon switches on and off correctly with the switch operation.

The supply is TT. All circuits are either R.C.D. or R.C.B.O. protected. No tripping off of anything is evident.

The only load that comes into play when the socket on the cooker control panel is switched on  is the neon indicator. Nothing is plugged into it.  Hardly a series supply for a large fan extractor hood. Surely it could not pass sufficient current.

A current sensing relay somewhere perhaps? The previous owner was a techi type person.

www.youtube.com/watch

Z.

The previous owner was a techi type person.

aha. That is a vital bit of info. Now I'd open the fan unit as well, and as well as looking for any extra trick boxes of eletroncis, put a meter on the incoming terminals. I like the idea of it sensing something, like current draw, or  heat or vapour from the hob to make turn it off when not needed.

The neon will draw about 1mA on it's own, and generates an arc like current waveform in minaiture, as the neon is more or less a perfect insulator up to about 80-90 volts but once struck is a low impedance, the current being largely determined by the series resistor, and only extinguishes when the voltage falls below 50-60V. You can use neon lamps to sense the environment, as it  moves these thresholds about a bit, but it is a very unreapeateble art, and I think we can ignore that,

Let us know what you find before you take it all out and make it conventional.

Mike.

The previous owner was a techi type person.

aha. That is a vital bit of info. Now I'd open the fan unit as well, and as well as looking for any extra trick boxes of eletroncis, put a meter on the incoming terminals. I like the idea of it sensing something, like current draw, or  heat or vapour from the hob to make turn it off when not needed.

The neon will draw about 1mA on it's own, and generates an arc like current waveform in minaiture, as the neon is more or less a perfect insulator up to about 80-90 volts but once struck is a low impedance, the current being largely determined by the series resistor, and only extinguishes when the voltage falls below 50-60V. You can use neon lamps to sense the environment, as it  moves these thresholds about a bit, but it is a very unreapeateble art, and I think we can ignore that,

Let us know what you find before you take it all out and make it conventional.

Mike.