Sluggish radiators - Please help

[MissMolly5]

I have recently taken on a three storey house with gas central heating system. There are two rads in the kitchen which is on the ground floor. These rads are sluggish and no-one seems to know what the problem is! The symptoms are;
Take much longer to heat than the others in the property
One valve is scorching hot, whereas the other is only just warm - almost cold, regardless of the temp of the rad
The rads heat from the top down but the bottom never really gets as hot as the rest
They don't need bleeding as they are hot at the top. The system has recently been balanced and the boiler has had a new pump. They do eventually get hot but I'm talking an hour (maybe longer) after the heatings been cranked up.
Please bear in mind I have very little knowledge about plumbing or DIY in general, but any advice would be greatly received. I'm new to this whole DIY world but eager to learn
Also, can anyone advice whether my sluggish rads will be having a negative effect on the rest of the system?

 

[Hugh Jaleak]

Quite possible the system is getting choked up with sludge. Heating systems contain a mixture of metals, wherein the water acts as an electrolyte allowing a chemical reaction to take place, slowly dissolving the metal. This reaction creates a black oxide sludge, which can slowly block the system.

Assuming this is the case, (black water when bleeding a rad is a good indicator), the system needs cleaning out. Options are chemical flush, (possible DIY job), or powerflush, (professional job). What type of system do you have? Make/model of boiler, have you any water tanks and/or hot water cylinder.

 

[ajrobb]

Have a look at Sentinel X400 system restorer. Then Sentinel X100 inhibitor. You'll see these discussed quite a bit on this forum.

When radiators are balanced, the aim is to adjust the lock shield valves so that all the radiators warm up quickly and end up with the same temperature drop (usually either 11°C or 20°C) between flow and return valves with any TRVs open. If the radiators are generously sized, a temperature drop (delta-T) of 20°C is sometimes used to try to improve condensing boiler efficiency. However, the radiators will warm up quicker and heat better with a delta-T of 11°C.

You could just try opening the lock shield valves an extra quarter turn on the troublesome radiators.

 

[MissMolly5]

Combi boiler system with an Ideal boiler (which has caused me endless problems). System was put in from new and property was only built in 2006. Should I be experiencing sludge/blockage problems when system is only four years old?

 

[Hugh Jaleak]

System sounds rather young to have an excessive sludge problem, especially as it should have had inhibitor added at installation. Boiler could well be the culprit, where abouts is it in the property? (As you've found out unfortunately, Ideal boilers dont exactly live up to their name.....)

The problem you have wont cause a negative effect on the rest of the system, its just annoying. (And cold in affected rooms no doubt.) You could try turning off all other rads and see if the kitchen rads work any better. Also, if there are Thermostatic valves fitted, remove the head and check pins are free to move up/down.