The last Hendy boiler I worked on had an ignition pack that showed a green light when the heater was running fine and flashed a set number of times for the fault identification. If your heater is the same as the one I worked on then I would first check and make sure that (a) there is in fact power being supplied to the power pack, (b) that the fuse contained within the power pack has not blown.
Depending where you are in the World as your post does not tell me which Country you are in there is another option that is quite a frequent cause of electronic failure here in New Zealand and that would be to fit a Voltage Dependant Resistor or a power spike protector to stop 240 voltage spikes which can easily cause a power pack to fail. Most important to fit if you reside in the backblocks and often get power outages or power surges.
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians