Zone valve start, the circulating pump is going, pilot is on but no combustion on my boiler. Any concept? ...

Do they if truth be told put ink...
If it is a standing pilot unit the thermocouple could be doomed to failure. It could also be a problem with the glorious limit or the aquastat. For a troubleshooting guide, check out my source.

Pet Stain Removal on Cement Porch/Deck?
All the delivery systems are working but it sounds approaching (with no combustion) there is no hot wet to deliver.
If your boiler (gas) isn't firing, the jets could be clogged not allowing the gas to flow to the pilot or (oil) in that is a prob with the gun not shooting grease into the chamber and needs cleaning.
Keep heat,.
What are the costs per m2 for plastering...
Answers:    Sounds like a dirty/faulty flame sensor. Look for a metallic sensor near a porcelin base. Shut everything down and verbs the metallic part beside some steel wool or fine sandpaper. BE CAREFUL! This is a fragile item! You only want to verbs it, not remove metal. Make sure the connections to and from it are tight and try relighting. This ought to help. If not, it could be a gas spigot or a safety component. Your best bet would be to call for in a tech. Hope this help!