Ravenheat CSI 85

[Jazzynash]

Have been working on a Ravenheat CSI 85 combi-condensing problem is on DHW boiler fires up for about 5 seconds then turns off repeating this I have carried out the following checks thermistors getting 12-15k ,found diverter valve passing,condense trap clear,min & max burner pressures ok, working pressure at gas metre is ok not sure if problem is plate to plate heat exchanger or does this have any pots on Pcb that may need adjusting would appreciate your thoughts.

Ps boiler fine on central heating

Thanx

 

[Slugbabydotcom]

Read my post HERE about condensate trap.
Trouble with thermistors is that they can go out of sync at different temps. I carry a spare to try in situ to help me eliminate what is a common cause of short cycling on these. BTW its 95% of the time that the CH thermistor causes the problem.
Does the boiler have 2 lights on the front or 3?
On earlier types with 3 lights sometimes its the ignition board, more commonly the blue SIT than the Red Honeywell
Does the fan spin freely?
Is the flue ok?
Is it worse when its windy?
Is there any flame lift?