hoval top gas boiler fault

[portrush25]

hoval boiler was running for a while and stopping reset and runs again for a couple of hours and so on now has stopped and showing e 16 fault can any one help please

 

[Anton]

This is from the list of fault codes supplied by Hoval. (I don't know anything about this mfr or their appliances, googled it)
E 16 Internal error in the firing device

 

[SimonJohns]

If your a GSR post it in there and I'll talk you through it