Delchi Fan assisted Radiators

I am not familiar with this make but the ones in our church (Myson and Dunham Bush) slow the fan by feeding it through a resistor (330 ohm for the two speeds). I've rewired the heaters so that the stat on the heater shorts out the resistance: i.e. it runs at high speed until fairly warm then drops to low speed. The boiler is controlled by a CM67 and the fan convector low-limit stat cuts off the fan when the water is cold.

There appear to be two fans and the circuit shows both phases going into a switch and four wires going out to the fan controller (which has a choke, etc.). I haven't yet spent the time trying to work out how it is wired without the switch - whoever did it included two thermostats in each blower, one which appears to be set to only allow the blower to start when the water temperature reaches a given preset and the other to cut out the blower if the ambient temperature is too high (I think). That means that there is a junction box in each which has mains in, two sets of thermostat cables and the cable to the fans - unfortunately these are all squeezed through glands making it hard to move the cover clear enough to see what wires go where!

I am inclined to knock out the two internal thermostats (the whole system has a room thermostat) and then see whether I can deduce what the motor switching would need to be. It will also allow me to find out why two of the units fans seem to have stopped working - if it is a motor/fan fault then I will be needing spares - anyone know a UK dealer?

Thanks