Large C/H system with cold rads on top floor

[Marvelous]

I have a large c/h system with 24 rads of varying sizes and with varying types (some cast iron, some pressed steel, some new towel rads).
The 3 rads in the loft coversion are cold for at least 3 hours before only 1 of them gets warm. I have done the basics like bleeding and balancing, but still now joy.

To compound matters, the h/w does not heat up if the c/h is on.

System basics are Potterton boiler (40Kw apparently), Grundfos 15-60 pump.

Is a 2 pump system an option or should the existing pump cope?

 

[twgas]

What model boiler, is system open or sealed, has any work been done on system recently, have the 3 rads ever worked properly?

 

[Marvelous]

Not sure of the model of boiler as it looks quite old, but it is a floor standing unit with 28mm flow and return. It is a gas boiler.

The system is vented and was worked on a while ago in the summer to convert the rads upstairs from the h/w system to c/h. All seemed fine at the time. They tapped into the 28mm flow and returns about 8m from the boiler on the first floor and brought them up in 22mm upon reaching the second floor they were reduced to 15mm and further to each rad about 3m apart on the second floor.

The h/w has only become a problem I bled both systems because of the inactive rads.

 

[D_Hailsham]

Not sure of the model of boiler as it looks quite old, but it is a floor standing unit with 28mm flow and return. It is a gas boiler.

The front panel usually unclips, you will then be able to read the data label to get them model no and GC number.

The system is vented and was worked on a while ago in the summer to convert the rads upstairs from the h/w system to c/h.

Radiators on the hot water system??? Do you mean towel rails?

They tapped into the 28mm flow and returns about 8m from the boiler on the first floor and brought them up in 22mm upon reaching the second floor they were reduced to 15mm and further to each rad about 3m apart on the second floor.

That's OK.

With that number of radiators the pump may not be hefty enough. It all depends on the system layout. You should also check that the boiler gives enough heat for the total wattage of the radiators etc.