Is my Boilermate 2000 actually calling to boiler?

So we got back from holiday last Monday to find our boiler flashing red and no hot water (heating was off at this time of year).

Self-diagnosed the flashing red light on the boiler (a Potterton Suprima 60L) as a dead APS and got a plumber to come in and change this. No difference. Boiler starts up, fan starts up, doesn't ignite, boiler shuts down with rapid flashing light.

Plumber decides that the PCB may be shot (common issue on this boiler) and changes this. No difference.

Plumber has now decided that the Boilermate is not calling for hot water from the boiler.

How do we check this (plumber has not seen a Boilermate before)? I am sure the boiler would be flashing green or orange if it was simply waiting but it may be that it wants an initial request and initial ignition.

The Boilermate seems to be working ok but the temperature of the store is 28 (of course it needs hot water from the boiler). The DHW temp is 24. Of the 3 LEDs, only the first two are lit and none flash when I switch the store off and on again (according to the manual I think they are supposed to flash on start up?)

Also on the LCD panel, all 3 bars to the side were lit when I first checked it a few days ago. When the plumber was playing yesterday only the top two bars were lit and when I checked it late last night, only the middle bar was lit. Not sure what that means?

I had the thermostat set to the highest temp and the heating on full (not timed). I also then ran a hot tap, when I turned this on, I heard a click from somewhere as if a pump was engaging. The DHW temp immediately dropped to 18 (from 24). But I still got a cold water of course.

The boiler simply cycles, retrying every few minutes or so. I think it is the boiler at fault but finding it difficult to diagnose! We don't have the electronic switch (immersion) so have had no hot water for over a week now!

Any help anyone can give me would be much appreciated!

Many thanks
Mark

If your plumber can not work out if the BM 2000 is asking the boiler to fire up.
I would try another one.
Checked the boiler pump?
Checked if the unit is full.
Would pay you to read through the posts on the BM 2000's on here.
Mike