Ignition problem with Myson Apollo 50si.

[Exselfbuilder]

Ignition problem with Myson Apollo 50si., fanned flue, LPG.
I have an Apollo as above, about 18 years old, part of a dual fuel system, so it is expected to do less than half of the necessary work producing heat and hot water. Today it refuses to ignite. It was working OK yesterday, as it has done throughout the Winter. Set on the timer to come on this morning, it did not. I have not yet had time to take it apart, a quick try out shows that there is no ignition spark at the pilot, hense no pilot. The fan operates, the high/ low switch makes no difference.
If anyone can help, my questions are;- Any ideas on what I can try, or what the problem might be? The spark electrode and lead, and the ignition PCB are available on the net, but are they a good bet to be at fault?
At 18 years old, is it worth spending much money on? It has given good service up till now.
If not, any recommendations for a good replacement would be welcome. I could fit the replacement myself, I installed the present boiler and complete system.
Thanks in anticipation to anyone who can help, and a happy new year to all. Exselfbuilder

 

[Exselfbuilder]

It was the fan stuck. I removed it and replaced one of the bearings, the impeller was rusted solid on the shaft so I could not get to the bearing that end. Works now, for how long I wonder. Any advice on a replacement boiler still welcome.
With regard to my post of a year ago about tha LINK FUEL system, that was the main circuit board. I had it rebuilt by a friend of a friend,That is all well now.
EXSELFBUILDER