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?

With the boiler firing, I would go along and feel the pipes. If hot water is circulating, the pipes should be hot starting where they come out of the boiler. It a line up to a tee is hot, but the branch off the tee isn't, somewhere that brach is blocked.

After 2 years of the system never working, I think it is time to demand your money back and find somebody else to instal a system that will work. So much for call a professional.

Thanks for that, the engineer says he has been over the pipes and heat does seem to be circulating. He will be at my house again tonight and it would be great to be in a position of knowledge so I can't be fobbed off - again. Do you (or anyone) have any thoughts on what else could be causing the problem? From the research I have done, the potential answers I have come up with are:
- There is a blockage which hasn't been located.
- The rads have become unbalanced and need to be re-balanced.

Any help would be most welcome. Thanks.

PS - the system has been working fine up until the last 2 months though.

Each loop should have a balancing valve. By restricting the flow to the closer radiators, it gives more flow to the further ones. Somebody could have left them all mostly closed so none of the radiators got much flow. That would be so obvious, that anybody should have found and fixed the problem. So make the engineer explain why any pipes that aren't hot don't have flow.

No expert here, but familiar enough with hot water systems to be able to state that air is the most common blockage reason. Each time the system is opened allows air into the pipes that must be purged completely.

Do you notice that the radiators on the upper levels are usually the cold ones? This is because air will migrate to the highest level, and if enough, cause the water to be completely "blocked" as the small circ pumps are not strong enough to push a column of water through and push a column of air.

Even once a system is purged, or bled, of air pockets allowed in during assembly, water itself contains air bubbles that will collect over time. A typical maintenance program will include bleeding the radiators of air periodically. This is why the older cast iron radiators had bleeder valves to allow air that collected in the upper portion of radiators to escape.

I am not knowledgeable of systems enough to explain how to bleed or purge the air, if I was there in person I could figure it out, but that is not an option.

Seems you have several professionals working on the system, I would assume that my suggestion is academic since this is common installation procedure and one of the first items checked on a troubleshooting list.

But since I did not see this being addressed, just thought I would add my two cents, or pence, ( or is is Euros now)which ever is appropriate for the geographical location.

Tkrussel's idea of air in the system is exactly what would lead to the radiators being colder at the top as you said. I struggle with the idea that a professional examined the system and didn't take care of things like the balancing valves and bleeding the air. Better luck with today's engineer.

Thanks for your help guys. It sounds as though it should be straightforward, either air, sludge or unbalanced rads. Like you, I find it difficult to understand why it seems so problematic to fix it. The guy is in the house now, but getting a straight answer out of him is not easy. I will let you know how we go. Fingers crossed!

We have had the same problem our first boiler wasn't big enough to pump the heat around our 4 bed house (13 radiators) check that your boiler is the right capacity for the house size