ICOS HE12 boiler and central heating

[Nordone]

I moved into a new 3 storey 4 bedroom house 10 months ago and I have the above boiler servicing 11 radiators.

The radiators will only heat at the top 1/3 so that below that level they are luke warm unless I set the thermostat to at least 26c which is way too high to be running central heating.

I have had the central heating flushed and all the radiators balanced at least twice plus another 4 separate visits by the builders plumbers all have failed to rectify the problem. All the radiators have been bled so there is no air in them.

Any ideas as to why the radiators are not heating correctly?

 

[gas4you]

Is this on a sealed system, or open vent?

3 storey house, 11 rads, plus HW, seems pushing a bit for a 12Kw boiler to me

 

[jimstreet]

cancell my first one!!

 

[heatingman]

pump prop to small and pipework is undersized, expect each floor is piped in 15mm

 

[davebgas]

If that system needs flushing and its only 10months old then something is seriously wrong...... I'd be checking the system is correctly balanced first, is it a Wimpey house by any chance??? 11 Rads and DHW as mentioned is alot for a 12KW.... could be sneaky and change the pins on the pcb to 'uprate' it but that would ne naughty

 

[johnfox]

by pass valve could be diverting heated water back to boiler to soon.
so can the output of an ixxs be increased by changing position of jumpers,very interesting.but system needs correct design aswell.
still very interesting.
i have seen most auto bypass valves not set up at all,just left the way they came supplied boxed.
usually fully open then return temp will be higher sooner as less resistance through bypass espically in a 3 storey property.
still interesting.

 

[Nordone]

It's a Barratt house.

It's been balanced twice in the last 2 months.

All the radiators are single, all the bedrooms are proper double bedrooms and the radiators in the 2 biggest are w - 700 H - 450 d - 70.