My Vokera Excell 80SP has developed a fault in which I have no hot water or central heating. The pilot light is lit and the fan runs. When the hot water or central heating is turned on the 3 port diverter valve and the primary flow switch activate, the pump and fan both run but the boiler fails to fire up. I have received a reply to suggest the primary flow switch diaphragm may have failed but this doesn't seem to be the case as it appears to be operating correctly. Is there a simple/cheap fix? I am very grateful for all the replies.

Wayne, June 2011

this sounds as if you are not getting gas to the burner, ok pilot light on, so gas to boiler, But it is not switching the gas to full burner. Cheap, probably not that cheap, you need to get someone that knows.
Without doing a series of checks, difficult to say where fault lies, you say primary flow is ok, But is it? might seem to operate, But does it? As you have gone as far as you are able, get someone in, expensive I know, But what choice?

SD, June 2011