Can leak sealer block the Pulsacoil 2000 boiler?

I have a 9 year old pulsacoil 2000 that had few issues fixed in the past few months. After the last engineer attendance all was working fine, he did recommend on his last visit however to pour the leak sealer to the tank to prevent further small leaks that apparently caused previous problems. So couple of months later I did buy the sealer and poured into the tank. 4 days after that my boiler stopped heating up and as a result i have very cold water coming out of my tap. Subconsciously I did associate this new issue with the sealer and decided to clear the tank of the water with the solution. So i filled the tank with clean water. Unfortunately the sealer is in the system now, so changing the water didn't improve the situation much. There is a pattern though. I've noticed that the boiler goes on at pre-set time and seems to be heating up, but then stops. Then tries again and stops again and so on. Each day though it seems to be working longer that on the previous day. As a result I have lukewarm water for one or two minutes and then it goes cold again.
I've already contacted the engineer, but thought that maybe there's something I could do myself to solve this in order to avoid his visit??
Many thanks

Arleta
January 2015