Poor Circulation

[Jimmylad]

My house is approx 10 years old and has a central heating system using 10mm plastic piping. For the last 5 years the system has had to be regularly power flushed once or twice a year due to 'magnetite' build up.
It was very rare that all rads were up to heat. To improve the circulation I reconfigured the existing 2 leg 2 pipe (feed & return) system to a 2 pipe figure of eight system and now I've lost all heat to my downstairs rads!! I have heat to the thermostatic valves but no heat in any of the rads (just slightly aired). I've replaced all the thermostatic and lockshield valves, reverse flushed all 13 rads and replaced as much of the old 10mm dia pipe as possible (not downstairs due to restrictions in cavity walls). I've balanced all upstairs rads (12 degree C diff). New water pumps have also been installed. What have I done wrong. Early answers appreciated, I'm getting severe grief from the missus

 

[mlcinfl]

Oh Jimmy, If your system has to be "powerflushed" every year then you have a serious pipework configuration problem that can't possibly be answered on a forum.
A 10 year old system that was correctly installed and commissioned should never need to be "powerflushed".
Ask your friends or colleagues to recommend a reputable Heating Engineer to take a look. If you don't get this problem dealt with soon you will be looking at replacing the entire system.
10mm plastic?? Oh boy. Whoever invented microbore should be hung, drawn and made to watch East Enders.

 

[swbjackson]

I can't picture what a figure of 8 pipework configuration is. I suspect your pipework is incorrect. If only your upstairs rads work you may have inadvertently converted it to a sinle pipe system.

 

[Jimmylad]

Thanks for the comments so far. To answer Swbjackson's query, originally one leg of the 2 pipe system fed the rad's at the front of the house and the second leg fed the rad's at the rear of the house. To 'improve' the flow I connected the ends of both legs to form a ring and then from there ran another pipe back to the boiler to form a figure '8' configuration. My thinking was that if a single pipe wasn't man enough to handle the flow then the figure of '8' would allow flow from two directions.

 

[swbjackson]

Sounds like that's your problem then. The water will follow the easiest route so it is bypassing the downstairs radiators completely. As you've formed a loop there is no way of balancing it.