Wallas burner trouble - flame sensor?

[roaringgirl]

When switched on the clicking of the pump seems to take too long to start, then at around 4 minutes in to startup, it's giving out a bit of heat, and then when I'd normally expect the glow plug to switch off and the thing to keep burning, it goes in to shutdown.

The pump is definitely supplying diesel as there was an excess of it in the burner when I took it apart. I replaced the glow-plug while I was there and it didn't fix the problem. I think what must be happening is that the flame sensor is bust, so the unit thinks it has failed to ignite.

Does anyone have any other ideas?

Does anyone know how to test the flame sensor with a multimeter?

 

[spannerman]

Sounds about right, if you use an ohm meter between the two wires and heat the sensor with a lighter it should either go open circuit or closed circuit depending on what it is when cold.

 

[roaringgirl]

Sounds about right, if you use an ohm meter between the two wires and heat the sensor with a lighter it should either go open circuit or closed circuit depending on what it is when cold.

I replaced the flame sensor and it worked on the bench, put it all back together and now it doesn't!

 

[roaringgirl]

Update: it *was* the flame sensor. I replaced it, now it works. We now carry a spare flame sensor.