Ravenheat csi85 woes

I for my sins have a ravenheat csi 85 combi boiler and it has been a pig for years. Recently the pump has been making lots of noise and last week I woke up to a cold house, but the hot water worked. So a refurbished wilo pump was ordered and I replaced the old one (head unit replacement) the old one had lots of lateral play and also one of the bearings appeared shot. But the heating still didn't work. For those unfamiliar with this boiler there is nothing as nice as error codes!
A Quick check that the hot water still worked, yep, diverter valve pin moves hits micro switch all works. So I buy a CH sensor and a pressure switch, cheap as chips replace them and still no heating, nothing whatsoever, no boiler firing, no pump running (no 240v to the pump) and now the hot water is playing up!!
It is cycling, open tap, burners light, 3 seconds , burners go out, repeat.
Aghhhhh I hate ravenheat.

Only because I can get one for £35 ive ordered a main pcb.
Have I missed anything obvious?
Ive checked that pressure switch is working (with multimeter) and ch over heat sensor, flue fan is running fine
Any suggestions, apart from the obvious bin this junk
Thanks for reading

If the diverter is working ok then is the flow pipe getting hot.

I can watch the pin from the diverter move out as a hot tap is turned on and operate the microswitch. The burnerscignite but go out after a 2 or 3 seconds cycling about every 10 to 15 seconds
Im at work atm but I did put my hand into the flow of water from the hot tap, whilst it was not hot or tepid, it was slightly warmer than the cold water flow
Pcb arrives in the morning
If its still dead think ill bite the bullet and order a vitodens100 35kw

I used to have an RFS-84, which I think was the non-condensing model... so probably common heritage. A terrible fault I had was cycling, and changing the sensors and PCB made no difference. Had me stumped! Then, by accident, I noticed that the cabling between the sensors and the PCB, when wiggled, changed things. So the cable was faulty, rather than the sensor. So I had assumed the sensor was bad, because I was checking readings at the PCB, but a new sensor made no difference, as it was the wiring harness. So test that if you can.

Good call, ive got the schematic, and the pcb appears to be well labeled. So checking continuity of most sensor wires whilst fiddly shouldn't be too difficult. It would explain some of the random behaviour
I'll report back

Well found out why dhc was cycling
Stupid me assumed that the microswitch on the diverter was working because I could hear it click
We have hot water!!!
Now to figure out the heating, pcb arrives tomorrow