Hi
Is there any product on the market that I can introduce into my central heating system via the header tank to cure a blockage safely.
I have bled the system many times over the the last week or so but the rads downstairs go luke warm whilst up stairs they work perfectly well.
To get the lower rads to heat up I have to turn the pump from high to low several times which causes a water surge but after a short while they cool down again, also the boiler keeps firing on and off until I do this.

Thanks