No lights on Honeywell HCW80 relay unit

[AskFrank]

Hi,
My Honeywell HCW80 relay unit is not lighting up at all when I press or hold the button. I believe this fault is causing my central heating to have stopped. Looking behind the cover, things look fine, but I'm no expert. What would be the best course of action here?

Picture of the relay unit I'm on about:

 

[ianmcd]

you will have to remove the unit from the back plate and see if you are getting 240vAC between live and neutral, could someone have turned off the fused spur by mistake ?

 

[AskFrank]

you will have to remove the unit from the back plate and see if you are getting 240vAC between live and neutral, could someone have turned off the fused spur by mistake ?

Will I have to use one of these? https://www.screwfix.com/p/lap-mas830b-digital-multimeter-600v/75337
I will have to check around for a fused spur. There is one below the unit but it's for the boiler itself.

Could I try and connect some of the terminals in order to send an ignition signal to the boiler? If so, what object could I use?