Baxi 105he central heating problem

[plumbertom]

hey I have got a baxi 105he, when I am trying to run hot water it runs perfectly but as soon as I put central heating on the boiler goes off. it try to light up three times but without success. the fault is a gas fault. I have checked all temperature sensors, pump, and changed pcb board and I couldn't fix this boiler. I cleaned filters, differential pressure switch , I removed diverted valve and check if it is working.

any ideas? much appreciated thanks in advance.

 

[Poxi]

Sounds like the min gas pressure is out..

 

[diesel_ltd]

+ 1 on checking low gas pressure