Boiler wont start up after shutting down

I have a sealed yplan system and have recenlty had problems with the boiler (baxi solo 3pfl range 7 years old)shutting down (not overheat) and it will not start for quite a while and the rads have gone cold, I have had all the wiring checked out and passed, fitted a new diverter valve, fitted new thermo stats on boiler and roomstat, fitted new potentiometer and a new pump for good measure, the pressure in the vessel is ok, it can be as long as 30 mins before it re ignites and by that time the rads have gone cold, I have even tried it with the room stat turned up to 30 deg, I am at my wits end with this problem, any help or advice would be greatfully accepted.
Rick.B

Split the problem; run on heating only and see what happens, ditto for dhw
do you have a bypass?

Do you have the electrical caparbility to safetly check for 240v at the switch live terminal where the wires are atatched to the PCB?

This will show if the boiler is receiving a demand from DHW or CH, and would indicate that the fualt lies within the boiler.

bear in mind that the pump will run on for some 8 mins after the burner extinguishes

If you dont have the neccessary skill dont risk nackering the Solo 3 or your self, just try plan B (below)

Bit of a long shot but is the Air Pressure Switch sticking and not returning to the rest position for some time after the DHW/CH demand ceases.

When the boiler stops firing, and after the pump over run time has passed, you could temporarily create a demand by raising the room stat
set point.(turn it right up)

If the boiler does not fire, try giving the case a slap on the top right hand side, this may jar the APS and allow the boiler to respond to the demand from the room stat.

Tim

PS, Always remember, just because things have been checked, does not mean they are ok, all you know is that you have not found the fault, it happens to all of us.