Saunier Duval Thema Classic 24e - Will not fire!

Hello,

I have been working on the above boiler at a house. The boiler was losing pressure and there was a leak on the cold water inlet. The boiler was still working as long as the pressure was right etc.

I diagnosed the problem to be the PRV due to the relif pipe dripping.
I changed the part which has solved the problem but no the boiler dosen't Fire??
The boiler goes through its start up procedurewith the fan running and what seams like the gas valve opening but then it does not fire. Following that the red light flashes and the boiler cuts out.
I don't know if the PCB has been damaged but don't want to replace that if it isn't the right part.

Has anyone else had similar problems with this boiler???

this is something to ask in the CC forum part follow the link to get setup there you need your Gas safe id
//www.diynot.com/forums/viewtopic.php?t=114690

But have a look at how the process works fan aps gas valve.

Only parts a Gas safe engineer should tamper with

Before you change any parts carefully check that you have not damaged the wiring loom, a short to the casing will give exactly the fault you describe.
Also the prv will not fail on its own, depressurise the boiler and leave the drain off open, check the expansion vessel is inflated to 0.7 bar. if it is remove and unblock the flexible connection hose - these block just for fun.