Yes, you are right. I changed the glow plug and everything returned to normal. I guess it was full of dirt so it can't hold the glowing. By the way, is there any method to clean the glow plug to keep it working more time?.

I couldn't solve the problem with the tail rotor 'cause it was a rainy day and I had to leave the field . I will try next weekend.

Thank you very much about your offer of giving me your number but I'm in Spain (near Valencia, here in the mediteranean coast) and it will be a bit expensive. I have to save my money to buy glow plugs .

Best regards