I hope someone can please help. We have had problems with our heating system (2 years old) for the past 2 months and have had the people who installed it working to repair it.

First the boiler stopped working properly. After a new pump, heat exchanger and circuit board were fitted, the boiler began functioning properly again. Pump and heat exch were badly corroded. British Gas came out (I signed up to their maintenance plan) and advised it looked as though inhibitor had not been passed through the system at installation - given the level of corrosion after just 2 yrs. Our fitter insisted that inhibitor had been passed through at installation.

Although boiler functioning, heat was not getting to radiators properly. Some were hot (not as hot as they should be), some were freezing (ones furthest from boiler) and some were in between. All were cooler at the bottom of the rad than at the top. BG suspected a blockage somewhere in system.

Original guy then passed chemical through system and left it to run through for 3 days (the bottle says 3 weeks, BG said 2 weeks!). Came back, drained it down, put inhibitor in, refilled it and still same problem with rads.
Last night, he took all the rads off and cleaned them out. Also went over the pipes in the basement with a magnet and said that if there was sludge, the magnet would stick to the pipe to tell him where it was. The magnet didn't stick anywhere = no blockage in pipes. With all rads cleaned out and no blockage in pipes, we should be working then? But we still have exactly the same problem with some rads freezing, some warm and some in between. Between last night and this morning, every rad has got colder than it was.

Does anyone have any idea what the problem might be?