The yellow does sound like part of the problem. I changed the fuse under the expansion tank and when i turned the key on i could hear the kind of buzzing noise from the pump but not heard it since. I changed the thermostat today im just a little worried that i got the housing seal right as it was a nightmare to keep in place. Got a new cap and when i compared them the old one had well and truley gone. I got rid of my discovery because i was sick of fixing the bloody thing lol.