Honeywell programmer program

[winterdune]

Hi all,
Sorry the title should have said problem not program! My Honeywell ST6400C central heating and hot water programmer has just gone wrong. I took it off the base plate and cleaned out the dust then put it back and pressed reset.Now I can set the date and time and programme in the heating and water times but as soon as I go to "run programme" the display disappears and nothing fires up. Do you think this is a problem with the unit which will be fixed by getting a replacement? Or could it be a different electrical problem? It's going to be a bit hard to get a central heating engineer out at the moment so I'd like to fix it myself but I'm not going to muck about with electrics...
Many thanks
Sean

 

[muggles]

Could be a different problem but most likely the programmer. Replacement is an ST9400C, fits on the same backplate so no rewiring required

 

[D_Hailsham]

Have you checked that all the terminals are done up tightly on the back plate? Turn the power off first!