On Sun, 28 Jun 2020 20:24:41 +0100, John Rumm
wrote:

On 28/06/2020 19:46, Mike McLeod wrote:
Just stopped working! No hot water or heating. Just won't fire-up for
some reason.

Worcester Greenstar Heatslave 18/25 oil-fired.

Got power to the controller board; no fuses blown. Any suggestions?

Start by checking that you are getting a call for heat right through to
the boiler. That will prove that the programmer, stats, and valve
microswitches are doing their stuff.

If by "boiler" you mean the actual burner, I can't get access to its
control box because of the bloody stupid construction of the boiler's
components. They've made it impossible to get the control box cover
off by juxtaposing it with (IIRC) the heat exchanger. If not the HE,
then something equally bulky and obstructive. I believe Worcesters are
notorious for this kind of poor internal layout.